RFC 3196 Internet Printing Protocol/1.1 November 20017.3 Response Headers............................................ 867.4 Entity Headers............................................. 877.5 Optional support for HTTP/1.0............................... 887.6 HTTP/1.1 Chunking........................................... 887.6.1 Disabling IPP Server Response Chunking..................... 887.6.2 Warning About the Support of Chunked Requests.............. 888 References..................................................... 899 Authors' Addresses............................................. 9110 Description of the Base IPP Documents.......................... 9411 Full Copyright Statement....................................... 96
Tables
Table 1 - Summary of Printer operation attributes that sender MUST
supply ................................................. 8
Table 2 - Summary of Printer operation attributes that sender MAY
supply ................................................. 10
Table 3 - Summary of Job operation attributes that sender MUST
supply.................................................. 12
Table 4 - Summary of Job operation attributes that sender MAY
supply.................................................. 14
Table 5 - Printer operation response attributes................... 16
Table 6 - Examples of validating IPP version...................... 19
Table 7 - Rules for validating single values X against Z.......... 401. Introduction
IPP is an application level protocol that can be used for distributed
printing using Internet tools and technologies. This document
contains information that supplements the IPP Model and Semantics
[RFC2911] and the IPP Transport and Encoding [RFC2910] documents. It
is intended to help implementers understand IPP/1.1, as well as
IPP/1.0 [RFC2565, RFC2566], and some of the considerations that may
assist them in the design of their client and/or IPP object
implementation. For example, a typical order of processing requests
is given, including error checking. Motivation for some of the
specification decisions is also included.
This document obsoletes RFC 2639 which was the Implementor's Guide
for IPP/1.0. The IPP Implementor's Guide (IIG) (this document)
contains information that supplements the IPP Model and Semantics
[RFC2911] and the IPP Transport and Encoding [RFC2910] documents.
This document is just one of a suite of documents that fully define
IPP. The base set of IPP documents includes:
Design Goals for an Internet Printing Protocol [RFC2567]
Rationale for the Structure and Model and Protocol for the
Internet Printing Protocol [RFC2568]
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RFC 3196 Internet Printing Protocol/1.1 November 2001
Internet Printing Protocol/1.1: Model and Semantics [RFC2911]
Internet Printing Protocol/1.1: Encoding and Transport [RFC2910]
Internet Printing Protocol/1.1: Implementor's Guide (this
document)
Mapping between LPD and IPP Protocols [RFC2569]
See section 10 for a description of these base IPP documents. Anyone
reading these documents for the first time is strongly encouraged to
read the IPP documents in the above order.
As such the information in this document is not part of the formal
specification of IPP/1.1. Instead information is presented to help
implementers understand IPP/1.1, as well as IPP/1.0 [RFC2565,
RFC2566], including some of the motivation for decisions taken by the
committee in developing the specification. Some of the
implementation considerations are intended to help implementers
design their client and/or IPP object implementations. If there are
any contradictions between this document and [RFC2911] or [RFC2910],
those documents take precedence over this document.
Platform-specific implementation considerations will be included in
this guide as they become known.
Note: In order to help the reader of the IIG and the IPP Model and
Semantics document, the sections in this document parallel the
corresponding sections in the Model document and are numbered the
same for ease of cross reference. The sections that correspond to
the IPP Transport and Encoding are correspondingly offset.
1.1 Conformance language
Usually, this document does not contain the terminology MUST, MUST
NOT, MAY, NEED NOT, SHOULD, SHOULD NOT, REQUIRED, and OPTIONAL.
However, when those terms do appear in this document, their intent is
to repeat what the [RFC2911] and [RFC2910] documents require and
allow, rather than specifying additional conformance requirements.
These terms are defined in section 12 on conformance terminology in
[RFC2911], most of which is taken from RFC 2119 [RFC2119].
Implementers should read section 12 (APPENDIX A) in [RFC2911] in
order to understand these capitalized words. The words MUST, MUST
NOT, and REQUIRED indicate what implementations are required to
support in a client or IPP object in order to be conformant to
[RFC2911] and [RFC2910]. MAY, NEED NOT, and OPTIONAL indicate was is
merely allowed as an implementer option. The verbs SHOULD and SHOULD
NOT indicate suggested behavior, but which is not required or
disallowed, respectively, in order to conform to the specification.
Hastings, et al. Informational [Page 5]

RFC 3196 Internet Printing Protocol/1.1 November 20011.2 Other terminology
This document uses other terms, such as "attributes", "operation",
and "Printer" as defined in [RFC2911] section 12. In addition, the
term "sender" refers to the client that sends a request or an IPP
object that returns a response. The term "receiver" refers to the
IPP object that receives a request and to a client that receives a
response.
1.3 Issues Raised from Interoperability Testing Events
The IPP WG has conducted three open Interoperability Testing Events.
The first one was held in September 1998, the second one was held in
March 1999, and the third one was held in October 2000. See the
summary reports in:
ftp://ftp.pwg.org/pub/pwg/ipp/new_TES/
The issues raised from the first Interoperability Testing Event are
numbered 1.n in this document and have been incorporated into
"IPP/1.0 Model and Semantics" [RFC2566] and the "IPP/1.0 Encoding and
Transport" [RFC2565] documents. However, some of the discussion is
left here in the Implementor's Guide to help understanding.
The issues raised from the second Interoperability Testing Event are
numbered 2.n in this document have been incorporated into "IPP/1.1
Model and Semantics" [RFC2911] and the "IPP/1.1 Encoding and
Transport" [RFC2910] documents. However, some of the discussion is
left here in the Implementor's Guide to help understanding.
The issues raised from the third Interoperability Testing Event are
numbered 3.n in this document and are described in:
ftp://ftp.pwg.org/pub/pwg/ipp/Issues/Issues-raised-at-Bake-Off3.pdfftp://ftp.pwg.org/pub/pwg/ipp/Issues/Issues-raised-at-Bake-Off3.docftp://ftp.pwg.org/pub/pwg/ipp/Issues/Issues-raised-at-Bake-Off3.txtHastings, et al. Informational [Page 6]

RFC 3196 Internet Printing Protocol/1.1 November 20012. IPP Objects
The term "client" in IPP is intended to mean any client that issues
IPP operation requests and accepts IPP operation responses, whether
it be a desktop or a server. In other words, the term "client" does
not just mean end-user clients, such as those associated with
desktops.
The term "IPP Printer" in IPP is intended to mean an object that
accepts IPP operation requests and returns IPP operation responses,
whether implemented in a server or a device. An IPP Printer object
MAY, if implemented in a server, turn around and forward received
jobs (and other requests) to other devices and print
servers/services, either using IPP or some other protocol.
3 IPP Operations
This section corresponds to Section 3 "IPP Operations" in the
IPP/1.1 Model and Semantics document [RFC2911].
3.1 Common Semantics
This section discusses semantics common to all operations.
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Job Operations
Requests Responses
Operation SD SU CJ GJA HJ All
Attributes (O) (O) (R) (R) RJ, RJ Opera-
(O+) tions
requesting-user- R R R R R
name
Legend:
SD: Send-Document
SU: Send-URI
CJ: Cancel-Job
GJA: Get-Job-Attributes
HJ, RJ, RJ: Hold-Job, Release-Job, Restart-Job
R indicates a REQUIRED operation that MUST be supported by the IPP
object (Printer or Job). For attributes, R indicates that the
attribute MUST be supported by the IPP object that supports the
associated operation.
O indicates an OPTIONAL operation or attribute that MAY be supported
by the IPP object (Printer or Job).
+ indicates that this is not an IPP/1.0 feature, but is only a part
of IPP/1.1 and future versions of IPP.
* "job-id" is REQUIRED only if used together with "printer-uri" to
identify the target job; otherwise, "job-uri" is REQUIRED.
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implementations MAY choose to be more forgiving than the error checks
shown here, in order to be able to accept requests from non-
conforming clients. Not performing all of these error checks is a
so-called "forgiving" implementation. On the other hand, clients
that successfully submit requests to IPP objects that do perform all
the error checks will be more likely to be able to interoperate with
other IPP object implementations. Thus an implementer of an IPP
object needs to decide whether to be a "forgiving" or a "strict"
implementation. Therefore, the error status codes returned may
differ between implementations. Consequentially, client SHOULD NOT
expect exactly the error code processing described in this section.
When an IPP object receives a request, the IPP object either accepts
or rejects the request. In order to determine whether or not to
accept or reject the request, the IPP object SHOULD execute the
following steps. The order of the steps may be rearranged and/or
combined, including making one or multiple passes over the request.
A client MUST supply requests that would pass all of the error checks
indicated here in order to be a conforming client. Therefore, a
client SHOULD supply requests that are conforming, in order to avoid
being rejected by some IPP object implementations and/or risking
different semantics by different implementations of forgiving
implementations. For example, a forgiving implementation that
accepts multiple occurrences of the same attribute, rather than
rejecting the request might use the first occurrences, while another
might use the last occurrence. Thus such a non-conforming client
would get different results from the two forgiving implementations.
In the following, processing continues step by step until a "RETURNS
the xxx status code ..." statement is encountered. Error returns are
indicated by the verb: "REJECTS". Since clients have difficulty
getting the status code before sending all of the document data in a
Print-Job request, clients SHOULD use the Validate-Job operation
before sending large documents to be printed, in order to validate
whether the IPP Printer will accept the job or not.
It is assumed that security authentication and authorization has
already taken place at a lower layer.
3.1.2.1 Suggested Operation Processing Steps for all Operations
This section is intended to apply to all operations. The next
section contains the additional steps for the Print-Job, Validate-
Job, Print-URI, Create-Job, Send-Document, and Send-URI operations
that create jobs, adds documents, and validates jobs.
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remains in a fixed position across all future versions so that all
clients and IPP object that support future versions can determine
which version is being used. The IPP object checks to see if the
major version number supplied in the request is supported. If not,
the Printer object REJECTS the request and RETURNS the 'server-
error-version-not-supported' status code in the response. The IPP
object returns in the "version-number" response attribute the major
and minor version for the error response. Thus the client can learn
at least one major and minor version that the IPP object supports.
The IPP object is encouraged to return the closest version number to
the one supplied by the client.
The checking of the minor version number is implementation dependent,
however if the client-supplied minor version is explicitly supported,
the IPP object MUST respond using that identical minor version
number. If the major version number matches, but the minor version
number does not, the Printer SHOULD accept and attempt to process the
request, or MAY reject the request and return the 'server-error-
version-not-supported' status code. In all cases, the Printer MUST
return the nearest version number that it supports. For example,
suppose that an IPP/1.2 Printer supports versions '1.1' and '1.2'.
The following responses are conforming:
Table 6 - Examples of validating IPP version
Client supplies Printer Accept Request? Printer returns
1.0 yes (SHOULD) 1.1
1.0 no (SHOULD NOT) 1.1
1.1 yes (MUST) 1.1
1.2 yes (MUST) 1.2
1.3 yes (SHOULD) 1.2
1.3 no (SHOULD NOT) 1.2
It is advantageous for Printers to support both IPP/1.1 and IPP/1.0,
so that they can interoperate with either client implementations.
Some implementations may allow an Administrator to explicitly disable
support for one or the other by setting the "ipp-versions-supported"
Printer description attribute.
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Likewise, it is advantageous for clients to support both versions to
allow interoperability with new and legacy Printers.
3.1.2.1.2 Validate operation identifier
The Printer object checks to see if the "operation-id" attribute
supplied by the client is supported as indicated in the Printer
object's "operations-supported" attribute. If not, the Printer
REJECTS the request and returns the 'server-error-operation-not-
supported' status code in the response.
3.1.2.1.3 Validate the request identifier
The Printer object SHOULD NOT check to see if the "request-id"
attribute supplied by the client is in range: between 1 and 2**31 - 1
(inclusive), but copies all 32 bits.
Note: The "version-number", "operation-id", and the "request-id"
parameters are in fixed octet positions in the IPP/1.1 encoding. The
"version-number" parameter will be the same fixed octet position in
all versions of the protocol. These fields are validated before
proceeding with the rest of the validation.
3.1.2.1.4 Validate attribute group and attribute presence and order
The order of the following validation steps depends on
implementation.
3.1.2.1.4.1 Validate the presence and order of attribute groups
Client requests and IPP object responses contain attribute groups
that Section 3 requires to be present and in a specified order. An
IPP object verifies that the attribute groups are present and in the
correct order in requests supplied by clients (attribute groups
without an * in the following tables).
If an IPP object receives a request with (1) required attribute
groups missing, or (2) the attributes groups are out of order, or (3)
the groups are repeated, the IPP object REJECTS the request and
RETURNS the 'client-error-bad-request' status code. For example, it
is an error for the Job Template Attributes group to occur before the
Operation Attributes group, for the Operation Attributes group to be
omitted, or for an attribute group to occur more than once, except in
the Get-Jobs response.
Since this kind of attribute group error is most likely to be an
error detected by a client developer rather than by a customer, the
IPP object NEED NOT return an indication of which attribute group was
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in error in either the Unsupported Attributes group or the Status
Message. Also, the IPP object NEED NOT find all attribute group
errors before returning this error.
3.1.2.1.4.2 Ignore unknown attribute groups in the expected position
Future attribute groups may be added to the specification at the end
of requests just before the Document Content and at the end of
response, except for the Get-Jobs response, where it maybe there or
before the first job attributes returned. If an IPP object receives
an unknown attribute group in these positions, it ignores the entire
group, rather than returning an error, since that group may be a new
group in a later minor version of the protocol that can be ignored.
(If the new attribute group cannot be ignored without confusing the
client, the major version number would have been increased in the
protocol document and in the request). If the unknown group occurs
in a different position, the IPP object REJECTS the request and
RETURNS the 'client-error-bad-request' status code.
Clients also ignore unknown attribute groups returned in a response.
Note: By validating that requests are in the proper form, IPP
objects force clients to use the proper form which, in turn,
increases the chances that customers will be able to use such clients
from multiple vendors with IPP objects from other vendors.
3.1.2.1.4.3 Validate the presence of a single occurrence of required Operation attributes
Client requests and IPP object responses contain Operation attributes
that [RFC2911] Section 3 requires to be present. Attributes within a
group may be in any order, except for the ordering of target,
charset, and natural languages attributes. These attributes MUST be
first, and MUST be supplied in the following order: charset, natural
language, and then target. An IPP object verifies that the
attributes that Section 4 requires to be supplied by the client have
been supplied in the request (attributes without an * in the
following tables). An asterisk (*) indicates groups and Operation
attributes that the client may omit in a request or an IPP object may
omit in a response.
If an IPP object receives a request with required attributes missing
or repeated from a group or in the wrong position, the behavior of
the IPP object is IMPLEMENTATION DEPENDENT. Some of the possible
implementations are:
REJECTS the request and RETURNS the 'client-error-bad-request'
status code
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accepts the request and uses the first occurrence of the attribute
no matter where it is
accepts the request and uses the last occurrence of the attribute
no matter where it is
accept the request and assume some default value for the missing
attribute
Therefore, client MUST send conforming requests, if they want to
receive the same behavior from all IPP object implementations. For
example, it is an error for the "attributes-charset" or "attributes-
natural-language" attribute to be omitted in any operation request,
or for an Operation attribute to be supplied in a Job Template group
or a Job Template attribute to be supplied in an Operation Attribute
group in a create request. It is also an error to supply the
"attributes-charset" attribute twice.
Since these kinds of attribute errors are most likely to be detected
by a client developer rather than by a customer, the IPP object NEED
NOT return an indication of which attribute was in error in either
the Unsupported Attributes group or the Status Message. Also, the
IPP object NEED NOT find all attribute errors before returning this
error.
The following tables list all the attributes for all the operations
by attribute group in each request and each response. The order of
the groups is the order that the client supplies the groups as
specified in [RFC2911] Section 3. The order of the attributes within
a group is arbitrary, except as noted for some of the special
operation attributes (charset, natural language, and target). The
tables below use the following notation:
R indicates a REQUIRED attribute or operation that an IPP
object MUST support
O indicates an OPTIONAL attribute or operation that an IPP
object NEED NOT support
* indicates that a client MAY omit the attribute in a request
and that an IPP object MAY omit the attribute in a response.
The absence of an * means that a client MUST supply the
attribute in a request and an IPP object MUST supply the
attribute in a response.
+ indicates that this is not a IPP/1.0 operation, but is only
a part of IPP/1.1 and future versions of IPP.
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Note 5: for the Get-Jobs operation the response contains a separate
Job Object Attributes group 3 to N containing requested-attributes
for each job object in the response.
3.1.2.1.5 Validate the values of the REQUIRED Operation attributes
An IPP object validates the values supplied by the client of the
REQUIRED Operation attribute that the IPP object MUST support. The
next section specifies the validation of the values of the OPTIONAL
Operation attributes that IPP objects MAY support.
The IPP object performs the following syntactic validation checks of
each Operation attribute value:
a) that the length of each Operation attribute value is correct
for the attribute syntax tag supplied by the client according
to [RFC2911] Section 4.1,
b) that the attribute syntax tag is correct for that Operation
attribute according to [RFC2911] Section 3,
c) that the value is in the range specified for that Operation
attribute according to [RFC2911] Section 3,
d) that multiple values are supplied by the client only for
operation attributes that are multi-valued, i.e., that are
1setOf X according to [RFC2911] Section 3.
If any of these checks fail, the IPP object REJECTS the request and
RETURNS the 'client-error-bad-request' or the 'client-error-request-
value-too-long' status code. Since such an error is most likely to
be an error detected by a client developer, rather than by an end-
user, the IPP object NEED NOT return an indication of which attribute
had the error in either the Unsupported Attributes Group or the
Status Message. The description for each of these syntactic checks
is explicitly expressed in the first IF statement in the following
table.
In addition, the IPP object checks each Operation attribute value
against some Printer object attribute or some hard-coded value if
there is no "xxx-supported" Printer object attribute defined. If its
value is not among those supported or is not in the range supported,
then the IPP object REJECTS the request and RETURNS the error status
code indicated in the table by the second IF statement. If the value
of the Printer object's "xxx-supported" attribute is 'no-value'
(because the system administrator hasn't configured a value), the
check always fails.
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RFC 3196 Internet Printing Protocol/1.1 November 2001
-----------------------------------------------
attributes-charset (charset)
IF NOT a single non-empty 'charset' value, REJECT/RETURN 'client-
error-bad-request'.
IF the value length is greater than 63 octets, REJECT/RETURN
'client-error-request-value-too-long'.
IF NOT in the Printer object's "charset-supported" attribute,
REJECT/RETURN "client-error-charset-not-supported".
attributes-natural-language(naturalLanguage)
IF NOT a single non-empty 'naturalLanguage' value, REJECT/RETURN
'client-error-bad-request'.
IF the value length is greater than 63 octets, REJECT/RETURN
'client-error-request-value-too-long'.
ACCEPT the request even if not a member of the set in the Printer
object's "generated-natural-language-supported" attribute. If the
supplied value is not a member of the Printer object's
"generated-natural-language-supported" attribute, use the Printer
object's "natural-language- configured" value.
requesting-user-name
IF NOT a single 'name' value, REJECT/RETURN 'client-error-bad-
request'.
IF the value length is greater than 255 octets, REJECT/RETURN
'client-error-request-value-too-long'.
IF the IPP object can obtain a better-authenticated name, use it
instead.
job-name(name)
IF NOT a single 'name' value, REJECT/RETURN 'client-error-bad-
request'.
IF the value length is greater than 255 octets, REJECT/RETURN
'client-error-request-value-too-long'.
IF NOT supplied by the client, the Printer object creates a name
from the document-name or document-uri.
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document-name (name)
IF NOT a single 'name' value, REJECT/RETURN 'client-error-bad-
request'.
IF the value length is greater than 255 octets, REJECT/RETURN
'client-error-request-value-too-long'.
ipp-attribute-fidelity (boolean)
IF NEITHER a single 'true' NOR a single 'false' 'boolean' value,
REJECT/RETURN 'client-error-bad-request'.
IF the value length is NOT equal to 1 octet, REJECT/RETURN
'client-error-request-value-too-long'
IF NOT supplied by the client, the IPP object assumes the value
'false'.
document-format (mimeMediaType)
IF NOT a single non-empty 'mimeMediaType' value, REJECT/RETURN
'client-error-bad-request'.
IF the value length is greater than 255 octets, REJECT/RETURN
'client-error-request-value-too-long'.
IF NOT in the Printer object's "document-format-supported"
attribute, REJECT/RETURN 'client-error-document-format-not-
supported'
IF NOT supplied by the client, the IPP object assumes the value of
the Printer object's "document-format-default" attribute.
document-uri (uri)
IF NOT a single non-empty 'uri' value, REJECT/RETURN 'client-
error-bad-request'.
IF the value length is greater than 1023 octets, REJECT/RETURN
'client-error-request-value-too-long'.
IF the URI syntax is not valid, REJECT/RETURN 'client-error-bad-
request'.
If the client-supplied URI scheme is not supported, i.e., the
value is not in the Printer object's referenced-uri-scheme-
supported" attribute, the Printer object MUST reject the request
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and return the 'client-error-uri-scheme-not-supported' status
code. The Printer object MAY check to see if the document exists
and is accessible. If the document is not found or is not
accessible, REJECT/RETURN 'client-error-not found'.
last-document (boolean)
IF NEITHER a single 'true' NOR a single 'false' 'boolean' value,
REJECT/RETURN 'client-error-bad-request'.
IF the value length is NOT equal to 1 octet, REJECT/RETURN
'client-error-request-value-too-long'
job-id (integer(1:MAX))
IF NOT an single 'integer' value equal to 4 octets AND in the
range 1 to MAX, REJECT/RETURN 'client-error-bad-request'.
IF NOT a job-id of an existing Job object, REJECT/RETURN 'client-
error-not-found' or 'client-error-gone' status code, if keep track
of recently deleted jobs.
requested-attributes (1setOf keyword)
IF NOT one or more 'keyword' values, REJECT/RETURN 'client-
error-bad-request'.
IF the value length is greater than 255 octets, REJECT/RETURN
'client-error-request-value-too-long'.
Ignore unsupported values, which are the keyword names of
unsupported attributes. Don't bother to copy such requested
(unsupported) attributes to the Unsupported Attribute response
group since the response will not return them.
which-jobs (type2 keyword)
IF NOT a single 'keyword' value, REJECT/RETURN 'client-error-bad-
request'.
IF the value length is greater than 255 octets, REJECT/RETURN
'client-error-request-value-too-long'.
IF NEITHER 'completed' NOR 'not-completed', copy the attribute and
the unsupported value to the Unsupported Attributes response group
and REJECT/RETURN 'client-error-attributes-or-values-not-
supported'.
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Note: a Printer still supports the 'completed' value even if it
keeps no completed/canceled/aborted jobs: by returning no jobs
when so queried.
IF NOT supplied by the client, the IPP object assumes the 'not-
completed' value.
my-jobs (boolean)
IF NEITHER a single 'true' NOR a single 'false' 'boolean' value,
REJECT/RETURN 'client-error-bad-request'.
IF the value length is NOT equal to 1 octet, REJECT/RETURN
'client-error-request-value-too-long'
IF NOT supplied by the client, the IPP object assumes the 'false'
value.
limit (integer(1:MAX))
IF NOT a single 'integer' value equal to 4 octets AND in the range
1 to MAX, REJECT/RETURN 'client-error-bad-request'.
IF NOT supplied by the client, the IPP object returns all jobs, no
matter how many.
-----------------------------------------------
3.1.2.1.6 Validate the values of the OPTIONAL Operation attributes
OPTIONAL Operation attributes are those that an IPP object MAY
support. An IPP object validates the values of the OPTIONAL
attributes supplied by the client. The IPP object performs the same
syntactic validation checks for each OPTIONAL attribute value as in
Section 3.1.2.1.5. As in Section 3.1.2.1.5, if any fail, the IPP
object REJECTS the request and RETURNS the 'client-error-bad-request'
or the 'client-error-request-value-too-long' status code.
In addition, the IPP object checks each Operation attribute value
against some Printer attribute or some hard-coded value if there is
no "xxx-supported" Printer attribute defined. If its value is not
among those supported or is not in the range supported, then the IPP
object REJECTS the request and RETURNS the error status code
indicated in the table. If the value of the Printer object's "xxx-
supported" attribute is 'no-value' (because the system administrator
hasn't configured a value), the check always fails.
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If the IPP object doesn't recognize/support an attribute, the IPP
object treats the attribute as an unknown or unsupported attribute
(see the last row in the table below).
-----------------------------------------------
document-natural-language (naturalLanguage)
IF NOT a single non-empty 'naturalLanguage' value, REJECT/RETURN
'client-error-bad-request'.
IF the value length is greater than 63 octets, REJECT/RETURN
'client-error-request-value-too-long'.
IF NOT a value that the Printer object supports in document
formats, (no corresponding "xxx-supported" Printer attribute),
REJECT/RETURN 'client-error-natural-language-not-supported'.
compression (type3 keyword)
IF NOT a single 'keyword' value, REJECT/RETURN 'client-error-bad-
request'.
IF the value length is greater than 255 octets, REJECT/RETURN
'client-error-request-value-too-long'.
IF NOT in the Printer object's "compression-supported" attribute,
REJECT/RETURN 'client-error-compression-not-supported'.
Note to IPP/1.0 implementers: Support for the "compression"
attribute was optional in IPP/1.0 and was changed to REQUIRED in
IPP/1.1. However, an IPP/1.0 object SHOULD at least check for the
"compression" attribute being present and reject the create
request, if they don't support "compression". Not checking is a
bug, since the data will be unintelligible.
job-k-octets (integer(0:MAX))
IF NOT a single 'integer' value equal to 4 octets, REJECT/RETURN
'client-error-bad-request'.
IF NOT in the range of the Printer object's "job-k-octets-
supported" attribute, copy the attribute and the unsupported value
to the Unsupported Attributes response group and REJECT/RETURN
'client-error-attributes-or-values-not-supported'.
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RFC 3196 Internet Printing Protocol/1.1 November 2001
job-impressions (integer(0:MAX))
IF NOT a single 'integer' value equal to 4 octets, REJECT/RETURN
'client-error-bad-request'.
IF NOT in the range of the Printer object's "job-impressions-
supported" attribute, copy the attribute and the unsupported value
to the Unsupported Attributes response group and REJECT/RETURN
'client-error-attributes-or-values-not-supported'.
job-media-sheets (integer(0:MAX))
IF NOT a single 'integer' value equal to 4 octets, REJECT/RETURN
'client-error-bad-request'.
IF NOT in the range of the Printer object's "job-media-sheets-
supported" attribute, copy the attribute and the unsupported value
to the Unsupported Attributes response group and REJECT/RETURN
'client-error-attributes-or-values-not-supported'.
message (text(127))
IF NOT a single 'text' value, REJECT/RETURN 'client-error-bad-
request'.
IF the value length is greater than 127 octets, REJECT/RETURN
'client-error-request-value-too-long'.
unknown or unsupported attribute
IF the attribute syntax supplied by the client is supported but
the length is not legal for that attribute syntax, REJECT/RETURN
'client-error-request-value-too-long'.
ELSE copy the attribute and value to the Unsupported Attributes
response group and change the attribute value to the "out-of-band"
'unsupported' value, but otherwise ignore the attribute.
Note: Future Operation attributes may be added to the protocol
specification that may occur anywhere in the specified group. When
the operation is otherwise successful, the IPP object returns the
'successful-ok-ignored-or-substituted-attributes' status code.
Ignoring unsupported Operation attributes in all operations is
analogous to the handling of unsupported Job Template attributes in
the create and Validate-Job operations when the client supplies the
"ipp-attribute-fidelity" Operation attribute with the 'false' value.
This last rule is so that we can add OPTIONAL Operation attributes to
future versions of IPP so that older clients can inter-work with new
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RFC 3196 Internet Printing Protocol/1.1 November 2001
IPP objects and newer clients can inter-work with older IPP objects.
(If the new attribute cannot be ignored without performing
unexpectedly, the major version number would have been increased in
the protocol document and in the request). This rule for Operation
attributes is independent of the value of the "ipp-attribute-
fidelity" attribute. For example, if an IPP object doesn't support
the OPTIONAL "job-k-octets" attribute', the IPP object treats "job-
k-octets" as an unknown attribute and only checks the length for the
'integer' attribute syntax supplied by the client. If it is not four
octets, the IPP object REJECTS the request and RETURNS the 'client-
error-bad-request' status code, else the IPP object copies the
attribute to the Unsupported Attribute response group, setting the
value to the "out-of-band" 'unsupported' value, but otherwise ignores
the attribute.
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RFC 3196 Internet Printing Protocol/1.1 November 20013.1.2.2.2 Check that the Printer object is accepting jobs
If the value of the Printer objects "printer-is-accepting-jobs" is
'false', the Printer object REJECTS the request and RETURNS the
'server-error-not-accepting-jobs' status code.
3.1.2.2.3 Validate the values of the Job Template attributes
An IPP object validates the values of all Job Template attribute
supplied by the client. The IPP object performs the analogous
syntactic validation checks of each Job Template attribute value that
it performs for Operation attributes (see Section 3.1.2.1.5.):
a) that the length of each value is correct for the attribute
syntax tag supplied by the client according to [RFC2911]
Section 4.1.
b) that the attribute syntax tag is correct for that attribute
according to [RFC2911] Sections 4.2 to 4.4.
c) that multiple values are supplied only for multi-valued
attributes, i.e., that are 1setOf X according to [RFC2911]
Sections 4.2 to 4.4.
As in Section 3.1.2.1.5, if any of these syntactic checks fail, the
IPP object REJECTS the request and RETURNS the 'client-error-bad-
request' or 'client-error-request-value-too-long' status code as
appropriate, independent of the value of the "ipp-attribute-
fidelity". Since such an error is most likely to be an error
detected by a client developer, rather than by an end-user, the IPP
object NEED NOT return an indication of which attribute had the error
in either the Unsupported Attributes Group or the Status Message.
The description for each of these syntactic checks is explicitly
expressed in the first IF statement in the following table.
Each Job Template attribute MUST occur no more than once. If an IPP
Printer receives a create request with multiple occurrences of a Job
Template attribute, it MAY:
1. reject the operation and return the 'client-error-bad-request'
error status code
2. accept the operation and use the first occurrence of the
attribute
3. accept the operation and use the last occurrence of the
attribute
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RFC 3196 Internet Printing Protocol/1.1 November 2001
depending on implementation. Therefore, clients MUST NOT supply
multiple occurrences of the same Job Template attribute in the Job
Attributes group in the request.
3.1.2.3 Algorithm for job validation
The process of validating a Job-Template attribute "xxx" against a
Printer attribute "xxx-supported" can use the following validation
algorithm (see section 3.2.1.2 in [RFC2911]).
To validate the value U of Job-Template attribute "xxx" against the
value V of Printer "xxx-supported", perform the following algorithm:
1. If U is multi-valued, validate each value X of U by performing the
algorithm in Table 7 with each value X. Each validation is
separate from the standpoint of returning unsupported values.
Example: If U is "finishings" that the client supplies with
'staple', 'bind' values, then X takes on the successive values:
'staple', then 'bind'
2. If V is multi-valued, validate X against each Z of V by performing
the algorithm in Table 7 with each value Z. If a value Z
validates, the validation for the attribute value X succeeds. If
it fails, the algorithm is applied to the next value Z of V. If
there are no more values Z of V, validation fails. Example" If V
is "sides-supported" with values: 'one- sided', 'two-sided-long',
and 'two-sided-short', then Z takes on the successive values:
'one-sided', 'two-sided-long', and 'two-sided-short'. If the
client supplies "sides" with 'two-sided- long', the first
comparison fails ('one-sided' is not equal to 'two-sided-long'),
the second comparison succeeds ('two-sided-long' is equal to
'two-sided-long"), and the third comparison ('two-sided-short'
with 'two-sided-long') is not even performed.
3. If both U and V are single-valued, let X be U and Z be V and use
the validation rules in Table 7.
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RFC 3196 Internet Printing Protocol/1.1 November 2001
Table 7 - Rules for validating single values X against Z
Attribute syntax attribute syntax validated if:
of X of Z
integer rangeOfInteger X is within the range of Z
uri uriScheme the uri scheme in X is equal to
Z
any boolean the value of Z is TRUE
any any X and Z are of the same type
and are equal.
If the value of the Printer object's "xxx-supported" attribute is
'no-value' (because the system administrator hasn't configured a
value), the check always fails. If the check fails, the IPP object
copies the attribute to the Unsupported Attributes response group
with its unsupported value. If the attribute contains more than one
value, each value is checked and each unsupported value is separately
copied, while supported values are not copied. If an IPP object
doesn't recognize/support a Job Template attribute, i.e., there is no
corresponding Printer object "xxx-supported" attribute, the IPP
object treats the attribute as an unknown or unsupported attribute
(see the last row in the table below).
If some Job Template attributes are supported for some document
formats and not for others or the values are different for different
document formats, the IPP object SHOULD take that into account in
this validation using the value of the "document-format" supplied by
the client (or defaulted to the value of the Printer's "document-
format-default" attribute, if not supplied by the client). For
example, if "number-up" is supported for the 'text/plain' document
format, but not for the 'application/postscript' document format, the
check SHOULD (though it NEED NOT) depend on the value of the
"document-format" operation attribute. See "document-format" in
[RFC2911] section 3.2.1.1 and 3.2.5.1.
Note: whether the request is accepted or rejected is determined by
the value of the "ipp-attribute-fidelity" attribute in a subsequent
step, so that all Job Template attribute supplied are examined and
all unsupported attributes and/or values are copied to the
Unsupported Attributes response group.
-----------------------------------------------
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RFC 3196 Internet Printing Protocol/1.1 November 2001
job-priority (integer(1:100))
IF NOT a single 'integer' value with a length equal to 4 octets,
REJECT/RETURN 'client-error-bad-request'.
IF NOT supplied by the client, use the value of the Printer
object's "job-priority-default" attribute at job submission time.
IF NOT in the range 1 to 100, inclusive, copy the attribute and
the unsupported value to the Unsupported Attributes response
group.
Map the value to the nearest supported value in the range 1:100 as
specified by the number of discrete values indicated by the value
of the Printer's "job-priority-supported" attribute. See the
formula in [RFC2911] Section 4.2.1.
job-hold-until (type3 keyword | name)
IF NOT a single 'keyword' or 'name' value, REJECT/RETURN 'client-
error-bad-request'.
IF the value length is greater than 255 octets, REJECT/RETURN
'client-error-request-value-too-long'.
IF NOT supplied by the client, use the value of the Printer
object's "job-hold-until" attribute at job submission time.
IF NOT in the Printer object's "job-hold-until-supported"
attribute, copy the attribute and the unsupported value to the
Unsupported Attributes response group.
job-sheets (type3 keyword | name)
IF NOT a single 'keyword' or 'name' value, REJECT/RETURN 'client-
error-bad-request'.
IF the value length is greater than 255 octets, REJECT/RETURN
'client-error-request-value-too-long'.
IF NOT in the Printer object's "job-sheets-supported" attribute,
copy the attribute and the unsupported value to the Unsupported
Attributes response group.
multiple-document-handling (type2 keyword)
IF NOT a single 'keyword' value, REJECT/RETURN 'client-error-bad-
request'.
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RFC 3196 Internet Printing Protocol/1.1 November 2001
IF the value length is greater than 255 octets, REJECT/RETURN
'client-error-request-value-too-long'.
IF NOT in the Printer object's "multiple-document-handling-
supported" attribute, copy the attribute and the unsupported value
to the Unsupported Attributes response group.
copies (integer(1:MAX))
IF NOT a single 'integer' value with a length equal to 4 octets,
REJECT/RETURN 'client-error-bad-request'.
IF NOT in range of the Printer object's "copies-supported"
attribute
copy the attribute and the unsupported value to the Unsupported
Attributes response group.
finishings (1setOf type2 enum)
IF NOT an 'enum' value(s) each with a length equal to 4 octets,
REJECT/RETURN 'client-error-bad-request'.
IF NOT in the Printer object's "finishings-supported" attribute,
copy the attribute and the unsupported value(s), but not any
supported values, to the Unsupported Attributes response group.
page-ranges (1setOf rangeOfInteger(1:MAX))
IF NOT a 'rangeOfInteger' value(s) each with a length equal to 8
octets, REJECT/RETURN 'client-error-bad-request'.
IF first value is greater than second value in any range, the
ranges are not in ascending order, or ranges overlap,
REJECT/RETURN 'client-error-bad-request'.
IF the value of the Printer object's "page-ranges-supported"
attribute is 'false', copy the attribute to the Unsupported
Attributes response group and set the value to the "out-of-band"
'unsupported' value.
sides (type2 keyword)
IF NOT a single 'keyword' value, REJECT/RETURN 'client-error-bad-
request'.
IF the value length is greater than 255 octets, REJECT/RETURN
'client-error-request-value-too-long'.
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RFC 3196 Internet Printing Protocol/1.1 November 2001
IF NOT in the Printer object's "sides-supported" attribute, copy
the attribute and the unsupported value to the Unsupported
Attributes response group.
number-up (integer(1:MAX))
IF NOT a single 'integer' value with a length equal to 4 octets,
REJECT/RETURN 'client-error-bad-request'.
IF NOT a value or in the range of one of the values of the Printer
object's "number-up-supported" attribute, copy the attribute and
value to the Unsupported Attribute response group.
orientation-requested (type2 enum)
IF NOT a single 'enum' value with a length equal to 4 octets,
REJECT/RETURN 'client-error-bad-request'.
IF NOT in the Printer object's "orientation-requested-supported"
attribute, copy the attribute and the unsupported value to the
Unsupported Attributes response group.
media (type3 keyword | name)
IF NOT a single 'keyword' or 'name' value, REJECT/RETURN 'client-
error-bad-request'.
IF the value length is greater than 255 octets, REJECT/RETURN
'client-error-request-value-too-long'.
IF NOT in the Printer object's "media-supported" attribute, copy
the attribute and the unsupported value to the Unsupported
Attributes response group.
printer-resolution (resolution)
IF NOT a single 'resolution' value with a length equal to 9
octets, REJECT/RETURN 'client-error-bad-request'.
IF NOT in the Printer object's "printer-resolution-supported"
attribute, copy the attribute and the unsupported value to the
Unsupported Attributes response group.
print-quality (type2 enum)
IF NOT a single 'enum' value with a length equal to 4 octets,
REJECT/RETURN 'client-error-bad-request'.
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RFC 3196 Internet Printing Protocol/1.1 November 2001
IF NOT in the Printer object's "print-quality-supported"
attribute, copy the attribute and the unsupported value to the
Unsupported Attributes response group.
unknown or unsupported attribute (i.e., there is no corresponding
Printer object "xxx-supported" attribute)
IF the attribute syntax supplied by the client is supported but
the length is not legal for that attribute syntax,
REJECT/RETURN 'client-error-bad-request' if the length of the
attribute syntax is fixed or 'client-error-request-value-too-long'
if the length of the attribute syntax is variable.
ELSE copy the attribute and value to the Unsupported Attributes
response group and change the attribute value to the "out-of-band"
'unsupported' value. Any remaining Job Template Attributes are
either unknown or unsupported Job Template attributes and are
validated algorithmically according to their attribute syntax for
proper length (see below).
-----------------------------------------------
If the attribute syntax is supported AND the length check fails,
the IPP object REJECTS the request and RETURNS the 'client-error-
bad-request' if the length of the attribute syntax is fixed or the
'client-error-request-value-too-long' status code if the length of
the attribute syntax is variable. Otherwise, the IPP object copies
the unsupported Job Template attribute to the Unsupported
Attributes response group and changes the attribute value to the
"out-of-band" 'unsupported' value. The following table shows the
length checks for all attribute syntaxes. In the following table:
"<=" means less than or equal, "=" means equal to:
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RFC 3196 Internet Printing Protocol/1.1 November 2001
Name Octet length check for read-write attributes
---------- ---------------------------------------------
'textWithLanguage <= 1023 AND 'naturalLanguage' <= 63
'textWithoutLanguage' <= 1023
'nameWithLanguage' <= 255 AND 'naturalLanguage' <= 63
'nameWithoutLanguage' <= 255
'keyword' <= 255
'enum' = 4
'uri' <= 1023
'uriScheme' <= 63
'charset' <= 63
'naturalLanguage' <= 63
'mimeMediaType' <= 255
'octetString' <= 1023
'boolean' = 1
'integer' = 4
'rangeOfInteger' = 8
'dateTime' = 11
'resolution' = 9
'1setOf X'
Note: It's possible for a Printer to receive a zero length keyword
in a request. Since this is a keyword, its value needs to be
compared with the supported values. Assuming that the printer
doesn't have any values in its corresponding "xxx-supported"
attribute that are keywords of zero length, the comparison will fail.
Then the request will be accepted or rejected depending on the value
of "ipp-attributes-fidelity" being 'false' or 'true', respectively.
No special handling is required for
3.1.2.3.1 Check for conflicting Job Template attributes values
Once all the Operation and Job Template attributes have been checked
individually, the Printer object SHOULD check for any conflicting
values among all the supported values supplied by the client. For
example, a Printer object might be able to staple and to print on
transparencies, however due to physical stapling constraints, the
Printer object might not be able to staple transparencies. The IPP
object copies the supported attributes and their conflicting
attribute values to the Unsupported Attributes response group. The
Printer object only copies over those attributes that the Printer
object either ignores or substitutes in order to resolve the
conflict, and it returns the original values which were supplied by
the client. For example suppose the client supplies "finishings"
equals 'staple' and "media" equals 'transparency', but the Printer
object does not support stapling transparencies. If the Printer
chooses to ignore the stapling request in order to resolve the
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RFC 3196 Internet Printing Protocol/1.1 November 2001
conflict, the Printer objects returns "finishings" equal to 'staple'
in the Unsupported Attributes response group. If any attributes are
multi-valued, only the conflicting values of the attributes are
copied.
Note: The decisions made to resolve the conflict (if there is a
choice) is implementation dependent.
3.1.2.3.2 Decide whether to REJECT the request
If there were any unsupported Job Template attributes or
unsupported/conflicting Job Template attribute values and the client
supplied the "ipp-attribute-fidelity" attribute with the 'true'
value, the Printer object REJECTS the request and return the status
code:
1.'client-error-conflicting-attributes' status code, if there were
any conflicts between attributes supplied by the client.
2.'client-error-attributes-or-values-not-supported' status code,
otherwise.
Note: Unsupported Operation attributes or values that are returned
do not affect the status returned in this step. If the unsupported
Operation attribute was a serious error, the above already rejected
the request in a previous step. If control gets to this step with
unsupported Operation attributes being returned, they are not serious
errors.
In general, the final results of Job processing are unknown at Job
submission time. The client has to rely on notifications or polling
to find out what happens at Job processing time. However, there are
cases in which some Printers can determine at Job submission time
that Job processing is going to fail. As an optimization, we'd like
to have the Printer reject the Job in these cases.
There are three types of "processing" errors that might be detectable
at Job submission time:
1. 'client-error-document-format-not-supported' : For the Print-
Job, Send-Document, Print-URI, and Send-URI operations, if all these
conditions are true:
- the Printer supports auto-sensing,
- the request "document-format" operation attribute is
'application/octet-stream',
- the Printer receives document data before responding,
- the Printer auto-senses the document format before responding,
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RFC 3196 Internet Printing Protocol/1.1 November 2001
- the sensed document format is not supported by the Printer
then the Printer should respond with 'client-error-document-format-
not-supported' status.
2. 'client-error-compression-error': For the Print-Job, Send-
Document, Print-URI, and Send-URI operations, if all these
conditions are true:
- the client supplies a supported value for the "compression"
operation attribute in the request
- the Printer receives document data before responding,
- the Printer attempts to decompress the document data before
responding,
- the document data cannot be decompressed using the algorithm
specified by the "compression" operation attribute
then the Printer should respond with 'client-error-compression-error'
status.
3. 'client-error-document-access-error': For the Print-URI, and
Send-URI operations, if the Printer attempts and fails to pull the
referenced document data before responding, it should respond with
'client-error-document-access-error' status.
Some Printers are not able to detect these errors until Job
processing time. In that case, the errors are recorded in the
corresponding job-state and job-state reason attributes. (There is
no standard way for a client to determine whether a Printer can
detect these errors at Job submission time.) For example, if auto-
sensing happens AFTER the job is accepted (as opposed to auto-sensing
at submit time before returning the response), the implementation
aborts the job, puts the job in the 'aborted' state and sets the
'unsupported-document-format' value in the job's "job-state-reasons".
A client should always provide a valid "document-format" operation
attribute whenever practical. In the absence of other information, a
client itself may sniff the document data to determine document
format.
Auto sensing at Job submission time may be more difficult for the
Printer when combined with compression. For auto-sensed Jobs, a
client may be better off deferring compression to the transfer
protocol layer, e.g.; by using the HTTP Content-Encoding header.
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RFC 3196 Internet Printing Protocol/1.1 November 20013.1.2.3.3 For the Validate-Job operation, RETURN one of the success status codes
If the requested operation is the Validate-Job operation, the Printer
object returns:
1. the "successful-ok" status code, if there are no unsupported or
conflicting Job Template attributes or values.
2. the "successful-ok-conflicting-attributes, if there are any
conflicting Job Template attribute or values.
3. the "successful-ok-ignored-or-substituted-attributes, if there
are only unsupported Job Template attributes or values.
Note: Unsupported Operation attributes or values that are returned
do not affect the status returned in this step. If the unsupported
Operation attribute was a serious error, the above already rejected
the request in a previous step. If control gets to this step with
unsupported Operation attributes being returned, they are not serious
errors.
3.1.2.3.4 Create the Job object with attributes to support
If "ipp-attribute-fidelity" is set to 'false' (or it was not supplied
by the client), the Printer object:
1. creates a Job object, assigns a unique value to the job's
"job-uri" and "job-id" attributes, and initializes all of the
job's other supported Job Description attributes.
2. removes all unsupported attributes from the Job object.
3. for each unsupported value, removes either the unsupported
value or substitutes the unsupported attribute value with some
supported value. If an attribute has no values after removing
unsupported values from it, the attribute is removed from the
Job object (so that the normal default behavior at job
processing time will take place for that attribute).
4. for each conflicting value, removes either the conflicting
value or substitutes the conflicting attribute value with some
other supported value. If an attribute has no values after
removing conflicting values from it, the attribute is removed
from the Job object (so that the normal default behavior at job
processing time will take place for that attribute).
If there were no attributes or values flagged as unsupported, or the
value of 'ipp-attribute-fidelity" was 'false', the Printer object is
able to accept the create request and create a new Job object. If
the "ipp-attribute-fidelity" attribute is set to 'true', the Job
Template attributes that populate the new Job object are necessarily
all the Job Template attributes supplied in the create request. If
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RFC 3196 Internet Printing Protocol/1.1 November 2001
the "ipp-attribute-fidelity" attribute is set to 'false', the Job
Template attributes that populate the new Job object are all the
client supplied Job Template attributes that are supported or that
have value substitution. Thus, some of the requested Job Template
attributes will not appear in the Job object because the Printer
object did not support those attributes. The attributes that
populate the Job object are persistently stored with the Job object
for that Job. A Get-Job-Attributes operation on that Job object will
return only those attributes that are persistently stored with the
Job object.
Note: All Job Template attributes that are persistently stored with
the Job object are intended to be "override values"; that is, they
that take precedence over whatever other embedded instructions might
be in the document data itself. However, it is not possible for all
Printer objects to realize the semantics of "override". End users
may query the Printer's "pdl-override-supported" attribute to
determine if the Printer either attempts or does not attempt to
override document data instructions with IPP attributes.
There are some cases, where a Printer supports a Job Template
attribute and has an associated default value set for that attribute.
In the case where a client does not supply the corresponding
attribute, the Printer does not use its default values to populate
Job attributes when creating the new Job object; only Job Template
attributes actually in the create request are used to populate the
Job object. The Printer's default values are only used later at Job
processing time if no other IPP attribute or instruction embedded in
the document data is present.
Note: If the default values associated with Job Template attributes
that the client did not supply were to be used to populate the Job
object, then these values would become "override values" rather than
defaults. If the Printer supports the 'attempted' value of the
"pdl-override-supported" attribute, then these override values could
replace values specified within the document data. This is not the
intent of the default value mechanism. A default value for an
attribute is used only if the create request did not specify that
attribute (or it was ignored when allowed by "ipp-attribute-fidelity"
being 'false') and no value was provided within the content of the
document data.
If the client does not supply a value for some Job Template
attribute, and the Printer does not support that attribute, as far as
IPP is concerned, the result of processing that Job (with respect to
the missing attribute) is undefined.
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RFC 3196 Internet Printing Protocol/1.1 November 20013.1.2.3.5 Return one of the success status codes
Once the Job object has been created, the Printer object accepts the
request and returns to the client:
1. the 'successful-ok' status code, if there are no unsupported or
conflicting Job Template attributes or values.
2. the 'successful-ok-conflicting-attributes' status code, if
there are any conflicting Job Template attribute or values.
3. the 'successful-ok-ignored-or-substituted-attributes' status
code, if there are only unsupported Job Template attributes or
values.
Note: Unsupported Operation attributes or values that are returned
do not affect the status returned in this step. If the unsupported
Operation attribute was a serious error, the above already rejected
the request in a previous step. If control gets to this step with
unsupported Operation attributes being returned, they are not serious
errors.
The Printer object also returns Job status attributes that indicate
the initial state of the Job ('pending', 'pending-held',
'processing', etc.), etc. See Print-Job Response, [RFC2911] section3.2.1.2.
3.1.2.3.6 Accept appended Document Content
The Printer object accepts the appended Document Content data and
either starts it printing, or spools it for later processing.
3.1.2.3.7 Scheduling and Starting to Process the Job
The Printer object uses its own configuration and implementation
specific algorithms for scheduling the Job in the correct processing
order. Once the Printer object begins processing the Job, the
Printer changes the Job's state to 'processing'. If the Printer
object supports PDL override (the "pdl-override-supported" attribute
set to 'attempted'), the implementation does its best to see that IPP
attributes take precedence over embedded instructions in the document
data.
3.1.2.3.8 Completing the Job
The Printer object continues to process the Job until it can move the
Job into the 'completed' state. If an Cancel-Job operation is
received, the implementation eventually moves the Job into the
'canceled' state. If the system encounters errors during processing
that do not allow it to progress the Job into a completed state, the
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implementation halts all processing, cleans up any resources, and
moves the Job into the 'aborted' state.
3.1.2.3.9 Destroying the Job after completion
Once the Job moves to the 'completed', 'aborted', or 'canceled'
state, it is an implementation decision as to when to destroy the Job
object and release all associated resources. Once the Job has been
destroyed, the Printer would return either the "client-error-not-
found" or "client-error-gone" status codes for operations directed at
that Job.
Note: the Printer object SHOULD NOT re-use a "job-uri" or "job-id"
value for a sufficiently long time after a job has been destroyed, so
that stale references kept by clients are less likely to access the
wrong (newer) job.
3.1.2.3.10 Interaction with "ipp-attribute-fidelity"
Some Printer object implementations may support "ipp-attribute-
fidelity" set to 'true' and "pdl-override-supported" set to
'attempted' and yet still not be able to realize exactly what the
client specifies in the create request. This is due to legacy
decisions and assumptions that have been made about the role of job
instructions embedded within the document data and external job
instructions that accompany the document data and how to handle
conflicts between such instructions. The inability to be 100%
precise about how a given implementation will behave is also
compounded by the fact that the two special attributes, "ipp-
attribute-fidelity" and "pdl-"override-supported", apply to the whole
job rather than specific values for each attribute. For example, some
implementations may be able to override almost all Job Template
attributes except for "number-up". Character Sets, natural
languages, and internationalization
This section discusses character set support, natural language
support and internationalization.
3.1.2.3.11 Character set code conversion support
IPP clients and IPP objects are REQUIRED to support UTF-8. They MAY
support additional charsets. It is RECOMMENDED that an IPP object
also support US-ASCII, since many clients support US-ASCII, and
indicate that UTF-8 and US-ASCII are supported by populating the
Printer's "charset-supported" with 'utf-8' and 'us-ascii' values. An
IPP object is required to code covert with as little loss as possible
between the charsets that it supports, as indicated in the Printer's
"charsets-supported" attribute.
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How should the server handle the situation where the "attributes-
charset" of the response itself is "us-ascii", but one or more
attributes in that response is in the "utf-8" format?
Example: Consider a case where a client sends a Print-Job request
with "utf-8" as the value of "attributes-charset" and with the "job-
name" attribute supplied. Later another client submits a Get-Job-
Attribute or Get-Jobs request. This second request contains the
"attributes-charset" with value "us-ascii" and "requested-attributes"
attribute with exactly one value "job-name".
According to the RFC2911 document (section 3.1.4.2), the value of the
"attributes-charset" for the response of the second request must be
"us-ascii" since that is the charset specified in the request. The
"job-name" value, however, is in "utf-8" format. Should the request
be rejected even though both "utf-8" and "us-ascii" charsets are
supported by the server? or should the "job-name" value be converted
to "us-ascii" and return "successful-ok-conflicting-attributes"
(0x0002) as the status code?
Answer: An IPP object that supports both utf-8 (REQUIRED) and us-
ascii, the second paragraph of section 3.1.4.2 applies so that the
IPP object MUST accept the request, perform code set conversion
between these two charsets with "the highest fidelity possible" and
return 'successful-ok', rather than a warning 'successful-ok-
conflicting-attributes, or an error. The printer will do the best it
can to convert between each of the character sets that it supports --
even if that means providing a string of question marks because none
of the characters are representable in US ASCII. If it can't perform
such conversion, it MUST NOT advertise us-ascii as a value of its
"attributes-charset-supported" and MUST reject any request that
requests 'us-ascii'.
One IPP object implementation strategy is to convert all request text
and name values to a Unicode internal representation. This is 16-bit
and virtually universal. Then convert to the specified operation
attributes-charset on output.
Also it would be smarter for a client to ask for 'utf-8', rather than
'us-ascii' and throw away characters that it doesn't understand,
rather than depending on the code conversion of the IPP object.
3.1.2.3.12 What charset to return when an unsupported charset is requested (Issue 1.19)?Section 3.1.4.1 Request Operation attributes was clarified in
November 1998 as follows:
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All clients and IPP objects MUST support the 'utf-8' charset
[RFC2044] and MAY support additional charsets provided that they are
registered with IANA [IANA-CS]. If the Printer object does not
support the client supplied charset value, the Printer object MUST
reject the request, set the "attributes-charset" to 'utf-8' in the
response, and return the 'client-error-charset-not-supported' status
code and any 'text' or 'name' attributes using the 'utf-8' charset.
Since the client and IPP object MUST support UTF-8, returning any
text or name attributes in UTF-8 when the client requests a charset
that is not supported should allow the client to display the text or
name.
Since such an error is a client error, rather than a user error, the
client should check the status code first so that it can avoid
displaying any other returned 'text' and 'name' attributes that are
not in the charset requested.
Furthermore, [RFC2911] section 14.1.4.14 client-error-charset-not-
supported (0x040D) was clarified in November 1998 as follows:
For any operation, if the IPP Printer does not support the charset
supplied by the client in the "attributes-charset" operation
attribute, the Printer MUST reject the operation and return this
status and any 'text' or 'name' attributes using the 'utf-8' charset
(see Section 3.1.4.1).
3.1.2.3.13 Natural Language Override (NLO)
The 'text' and 'name' attributes each have two forms. One has an
implicit natural language, and the other has an explicit natural
language. The 'textWithoutLanguage' and 'textWithLanguage' are the
two 'text' forms. The 'nameWithoutLanguage" and 'nameWithLanguage
are the two 'name' forms. If a receiver (IPP object or IPP client)
supports an attribute with attribute syntax 'text', it MUST support
both forms in a request and a response. A sender (IPP client or IPP
object) MAY send either form for any such attribute. When a sender
sends a WithoutLanguage form, the implicit natural language is
specified in the "attributes-natural-language" operation attribute,
which all senders MUST include in every request and response.
When a sender sends a WithLanguage form, it MAY be different from the
implicit natural language supplied by the sender or it MAY be the
same. The receiver MUST treat either form equivalently.
There is an implementation decision for senders, whether to always
send the WithLanguage forms or use the WithoutLanguage form when the
attribute's natural language is the same as the request or response.
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The former approach makes the sender implementation simpler. The
latter approach is more efficient on the wire and allows inter-
working with non-conforming receivers that fail to support the
WithLanguage forms. As each approach have advantages, the choice is
completely up to the implementer of the sender.
Furthermore, when a client receives a 'text' or 'name' job attribute
that it had previously supplied, that client MUST NOT expect to see
the attribute in the same form, i.e., in the same WithoutLanguage or
WithLanguage form as the client supplied when it created the job.
The IPP object is free to transform the attribute from the
WithLanguage form to the WithoutLanguage form and vice versa, as long
as the natural language is preserved. However, in order to meet this
latter requirement, it is usually simpler for the IPP object
implementation to store the natural language explicitly with the
attribute value, i.e., to store using an internal representation that
resembles the WithLanguage form.
The IPP Printer MUST copy the natural language of a job, i.e., the
value of the "attributes-natural-language" operation attribute
supplied by the client in the create operation, to the Job object as
a Job Description attribute, so that a client is able to query it.
In returning a Get-Job-Attributes response, the IPP object MAY return
one of three natural language values in the responses "attributes-
natural-language" operation attribute: (1) that requested by the
requester, (2) the natural language of the job, or (3) the configured
natural language of the IPP Printer, if the requested language is not
supported by the IPP Printer.
This "attributes-natural-language" Job Description attribute is
useful for an IPP object implementation that prints start sheets in
the language of the user who submitted the job. This same Job
Description attribute is useful to a multi-lingual operator who has
to communicate with different job submitters in different natural
languages. This same Job Description attribute is expected to be
used in the future to generate notification messages in the natural
language of the job submitter.
Early drafts of [RFC2911] contained a job-level natural language
override (NLO) for the Get-Jobs response. A job-level (NLO) is an
(unrequested) Job Attribute which then specified the implicit natural
language for any other WithoutLanguage job attributes returned in the
response for that job. Interoperability testing of early
implementations showed that no one was implementing the job-level NLO
in Get-Job responses. So the job-level NLO was eliminated from the
Get-Jobs response. This simplification makes all requests and
responses consistent in that the implicit natural language for any
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WithoutLanguage 'text' or 'name' form is always supplied in the
request's or response's "attributes-natural-language" operation
attribute.
3.1.3 Status codes returned by operation
This section corresponds to [RFC2911] section 3.1.6 "Operation
Response Status Codes and Status Messages". This section lists all
status codes once in the first operation (Print-Job). Then it lists
the status codes that are different or specialized for subsequent
operations under each operation.
3.1.3.1 Printer Operations3.1.3.1.1 Print-Job
The Printer object MUST return one of the following "status-code"
values for the indicated reason. Whether all of the document data
has been accepted or not before returning the success or error
response depends on implementation. See Section 13 in [RFC2911] for
a more complete description of each status code.
For the following success status codes, the Job object has been
created and the "job-id", and "job-uri" assigned and returned in the
response:
successful-ok: no request attributes were substituted or ignored.
successful-ok-ignored-or-substituted-attributes: some supplied
(1) attributes were ignored or (2) unsupported attribute syntaxes
or values were substituted with supported values or were ignored.
Unsupported attributes, attribute syntax's, or values MUST be
returned in the Unsupported Attributes group of the response.
successful-ok-conflicting-attributes: some supplied attribute
values conflicted with the values of other supplied attributes and
were either substituted or ignored. Attributes or values which
conflict with other attributes and have been substituted or
ignored MUST be returned in the Unsupported Attributes group of
the response as supplied by the client.
[RFC2911] section 3.1.6 Operation Status Codes and Messages states:
If the Printer object supports the "status-message" operation
attribute, it SHOULD use the REQUIRED 'utf-8' charset to return a
status message for the following error status codes (see section13 in [RFC2911]): 'client-error-bad-request', 'client-error-
charset-not-supported', 'server-error-internal-error', 'server-
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error-operation-not-supported', and 'server-error-version-not-
supported'. In this case, it MUST set the value of the
"attributes-charset" operation attribute to 'utf-8' in the error
response.
For the following error status codes, no job is created and no
"job-id" or "job-uri" is returned:
client-error-bad-request: The request syntax does not conform
to the specification.
client-error-forbidden: The request is being refused for
authorization or authentication reasons. The implementation
security policy is to not reveal whether the failure is one of
authentication or authorization.
client-error-not-authenticated: Either the request requires
authentication information to be supplied or the authentication
information is not sufficient for authorization.
client-error-not-authorized: The requester is not authorized
to perform the request on the target object.
client-error-not-possible: The request cannot be carried out
because of the state of the system. See also 'server-error-
not-accepting-jobs' status code, which MUST take precedence if
the Printer object's "printer-accepting-jobs" attribute is
'false'.
client-error-timeout: not applicable.
client-error-not-found: the target object does not exist.
client-error-gone: the target object no longer exists and no
forwarding address is known.
client-error-request-entity-too-large: the size of the request
and/or print data exceeds the capacity of the IPP Printer to
process it.
client-error-request-value-too-long: the size of request
variable length attribute values, such as 'text' and 'name'
attribute syntax's, exceed the maximum length specified in
[RFC2911] for the attribute and MUST be returned in the
Unsupported Attributes Group.
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supplied is not supported. The "document-format" attribute
with the unsupported value MUST be returned in the Unsupported
Attributes Group. This error SHOULD take precedence over any
other 'xxx-not-supported' error, except 'client-error-charset-
not-supported'.
client-error-attributes-or-values-not-supported: one or more
supplied attributes, attribute syntax's, or values are not
supported and the client supplied the "ipp-attributes-
fidelity" operation attribute with a 'true' value. They MUST
be returned in the Unsupported Attributes Group as explained
below.
client-error-uri-scheme-not-supported: not applicable.
client-error-charset-not-supported: the charset supplied in
the "attributes-charset" operation attribute is not supported.
The Printer's "configured-charset" MUST be returned in the
response as the value of the "attributes-charset" operation
attribute and used for any 'text' and 'name' attributes
returned in the error response. This error SHOULD take
precedence over any other error, unless the request syntax is
so bad that the client's supplied "attributes-charset" cannot
be determined.
client-error-conflicting-attributes: one or more supplied
attribute values conflicted with each other and the client
supplied the "ipp-attributes-fidelity" operation attribute with
a 'true' value. They MUST be returned in the Unsupported
Attributes Group as explained below.
server-error-internal-error: an unexpected condition prevents
the request from being fulfilled.
server-error-operation-not-supported: not applicable (since
Print-Job is REQUIRED).
server-error-service-unavailable: the service is temporarily
overloaded.
server-error-version-not-supported: the version in the request
is not supported. The "closest" version number supported MUST
be returned in the response.
server-error-device-error: a device error occurred while
receiving or spooling the request or document data or the IPP
Printer object can only accept one job at a time.
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server-error-temporary-error: a temporary error such as a
buffer full write error, a memory overflow, or a disk full
condition occurred while receiving the request and/or the
document data.
server-error-not-accepting-jobs: the Printer object's
"printer-is-not-accepting-jobs" attribute is 'false'.
server-error-busy: the Printer is too busy processing jobs to
accept another job at this time.
server-error-job-canceled: the job has been canceled by an
operator or the system while the client was transmitting the
document data.
3.1.3.1.2 Print-URI
All of the Print-Job status codes described in Section 3.1.3.1.1
Print-Job Response are applicable to Print-URI with the following
specializations and differences. See Section 14 for a more complete
description of each status code.
client-error-uri-scheme-not-supported: the URI scheme supplied
in the "document-uri" operation attribute is not supported and
is returned in the Unsupported Attributes group.
server-error-operation-not-supported: the Print-URI operation
is not supported.
3.1.3.1.3 Validate-Job
All of the Print-Job status codes described in Section 3.1.3.1.1
Print-Job Response are applicable to Validate-Job. See Section 13 in
[RFC2911] for a more complete description of each status code.
3.1.3.1.4 Create-Job
All of the Print-Job status codes described in Section 3.1.3.1.1
Print-Job Response are applicable to Create-Job with the following
specializations and differences. See Section 13 in [RFC2911] for a
more complete description of each status code.
server-error-operation-not-supported: the Create-Job operation
is not supported.
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client-error-multiple-document-jobs-not-supported: while the
Create-Job and Send-Document operations are supported, this
implementation doesn't support more than one document with
data.
3.1.3.1.5 Get-Printer-Attributes
All of the Print-Job status codes described in Section3.1.3.1.1 Print-Job Response are applicable to the Get-
Printer-Attributes operation with the following
specialization's and differences. See Section 13 in [RFC2911]
for a more complete description of each status code.
For the following success status codes, the requested
attributes are returned in Group 3 in the response:
successful-ok: no operation attributes or values were
substituted or ignored (same as Print-Job) and no requested
attributes were unsupported.
successful-ok-ignored-or-substituted-attributes: The
"requested-attributes" operation attribute MAY, but NEED NOT,
be returned with the unsupported values.
successful-ok-conflicting-attributes: same as Print-Job.
For the error status codes, Group 3 is returned containing no
attributes or is not returned at all:
client-error-not-possible: Same as Print-Job, in addition the
Printer object is not accepting any requests.
client-error-request-entity-too-large: same as Print-job,
except that no print data is involved.
client-error-attributes-or-values-not-supported: not
applicable, since unsupported operation attributes and/or
values MUST be ignored and an appropriate success code returned
(see above).
client-error-conflicting-attributes: same as Print-Job, except
that "ipp-attribute-fidelity" is not involved.
server-error-operation-not-supported: not applicable (since
Get-Printer-Attributes is REQUIRED).
server-error-device-error: same as Print-Job, except that no
document data is involved.
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server-error-temporary-error: same as Print-Job, except that
no document data is involved.
server-error-not-accepting-jobs: not applicable.
server-error-busy: same as Print-Job, except the IPP object is
too busy to accept even query requests.
server-error-job-canceled: not applicable.
3.1.3.1.6 Get-Jobs
All of the Print-Job status codes described in Section 3.1.3.1.1
Print-Job Response are applicable to the Get-Jobs operation with the
following specialization's and differences. See Section 13 in
[RFC2911] for a more complete description of each status code.
For the following success status codes, the requested attributes are
returned in Group 3 in the response:
successful-ok: same as Get-Printer-Attributes (see section3.1.3.1.5).
successful-ok-ignored-or-substituted-attributes: same as Get-
Printer-Attributes (see section 3.1.3.1.5).
successful-ok-conflicting-attributes: same as Get-Printer-
Attributes (see section 3.1.3.1.5).
For any error status codes, Group 3 is returned containing no
attributes or is not returned at all. The following brief error
status code descriptions contain unique information for use with
Get-Jobs operation. See section 14 for the other error status codes
that apply uniformly to all operations:
client-error-not-possible: Same as Print-Job, in addition the
Printer object is not accepting any requests.
client-error-request-entity-too-large: same as Print-job,
except that no print data is involved.
client-error-document-format-not-supported: not applicable.
client-error-attributes-or-values-not-supported: not
applicable, since unsupported operation attributes and/or
values MUST be ignored and an appropriate success code returned
(see above).
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client-error-conflicting-attributes: same as Print-Job, except
that "ipp-attribute-fidelity" is not involved.
server-error-operation-not-supported: not applicable (since
Get-Jobs is REQUIRED).
server-error-device-error: same as Print-Job, except that no
document data is involved.
server-error-temporary-error: same as Print-Job, except that
no document data is involved.
server-error-not-accepting-jobs: not applicable.
server-error-job-canceled: not applicable.
3.1.3.1.7 Pause-Printer
All of the Print-Job status codes described in Section 3.1.3.1.1
Print-Job Response are applicable to Pause-Printer with the following
specializations and differences. See Section 13 in [RFC2911] for a
more complete description of each status code.
For the following success status codes, the Printer object is being
stopped from scheduling jobs on all its devices.
successful-ok: no request attributes were substituted or
ignored (same as Print-Job).
successful-ok-ignored-or-substituted-attributes: same as
Print-Job.
successful-ok-conflicting-attributes: same as Print-Job.
For any of the error status codes, the Printer object has not been
stopped from scheduling jobs on all its devices.
client-error-not-possible: not applicable.
client-error-not-found: the target Printer object does not
exist.
client-error-gone: the target Printer object no longer exists
and no forwarding address is known.
client-error-request-entity-too-large: same as Print-Job,
except no document data is involved.
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client-error-document-format-not-supported: not applicable.
client-error-conflicting-attributes: same as Print-Job, except
that the Printer's "printer-is-accepting-jobs" attribute is not
involved.
server-error-operation-not-supported: the Pause-Printer
operation is not supported.
server-error-device-error: not applicable.
server-error-temporary-error: same as Print-Job, except no
document data is involved.
server-error-not-accepting-jobs: not applicable.
server-error-job-canceled: not applicable.
3.1.3.1.8 Resume-Printer
All of the Print-Job status code descriptions in Section 3.1.3.1.1
Print-Job Response with the specialization's described for Pause-
Printer are applicable to Resume-Printer. See Section 13 in
[RFC2911] for a more complete description of each status code.
For the following success status codes, the Printer object resumes
scheduling jobs on all its devices.
successful-ok: no request attributes were substituted or
ignored (same as Print-Job).
successful-ok-ignored-or-substituted-attributes: same as
Print-Job.
successful-ok-conflicting-attributes: same as Print-Job.
For any of the error status codes, the Printer object does not resume
scheduling jobs.
server-error-operation-not-supported: the Resume-Printer
operation is not supported.
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RFC 3196 Internet Printing Protocol/1.1 November 20013.1.3.1.8.1 What about Printers unable to change state due to an error condition?
If, in case, the IPP printer is unable to change its state due to
some problem with the actual printer device (say, it is shut down or
there is a media-jam as indicated in [RFC2911]), what should be the
result of the "Resume-Printer" operation? Should it still change the
'printer-state-reasons' and return success or should it fail ?
The Resume-Printer operation must clear the 'paused' or 'moving-to-
paused' 'printer-state-message'. The operation must return a
'successful-ok' status code.
3.1.3.1.8.2 How is "printer-state" handled on Resume-Printer?
If the Resume-Printer operation succeeds, what should be the value of
"printer-state" and who should take care of the "printer-state"
attribute value later on ?
The Resume-Printer operation may change the "printer-state-reasons"
value.
The "printer-state" will change to one of three states:
1. 'idle' - no additional jobs and no error conditions present
2. 'processing' - job available and no error conditions present
3. current state (i.e. no change) an error condition is present
(e.g. media jam)
In the third case the "printer-state-reason" will be cleared by
automata when it detects the error condition no longer exists. The
"printer-state" will move to 'idle' or 'processing' when conditions
permit. (i.e. no more error conditions)
3.1.3.1.9 Purge-Printer
All of the Print-Job status code descriptions in Section 3.1.3.1.1
Print-Job Response with the specialization's described for Pause-
Printer are applicable to Purge-Printer. See Section 13 in [RFC2911]
for a more complete description of each status code.
For the following success status codes, the Printer object purges all
it's jobs.
successful-ok: no request attributes were substituted or
ignored (same as Print-Job).
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successful-ok-ignored-or-substituted-attributes: same as
Print-Job.
successful-ok-conflicting-attributes: same as Print-Job.
For any of the error status codes, the Printer object does not purge
any jobs.
server-error-operation-not-supported: the Purge-Printer
operation is not supported.
3.1.3.2 Job Operations3.1.3.2.1 Send-Document
All of the Print-Job status codes described in Section 3.1.3.1.1
Print-Job Response are applicable to the Get-Printer-Attributes
operation with the following specialization's and differences. See
Section 13 in [RFC2911] for a more complete description of each
status code.
For the following success status codes, the document has been added
to the specified Job object and the job's "number-of-documents"
attribute has been incremented:
successful-ok: no request attributes were substituted or
ignored (same as Print-Job).
successful-ok-ignored-or-substituted-attributes: same as
Print-Job.
successful-ok-conflicting-attributes: same as Print-Job.
For the error status codes, no document has been added to the Job
object and the job's "number-of-documents" attribute has not been
incremented:
client-error-not-possible: Same as Print-Job, except that the
Printer's "printer-is-accepting-jobs" attribute is not
involved, so that the client is able to finish submitting a job
that was created with a Create-Job operation after this
attribute has been set to 'true'. Another condition is that
the state of the job precludes Send-Document, i.e., the job has
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already been closed out by the client. However, if the IPP
Printer closed out the job due to timeout, the 'client-error-
timeout' error status SHOULD be returned instead.
client-error-timeout: This request was sent after the Printer
closed the job, because it has not received a Send-Document or
Send-URI operation within the Printer's "multiple-operation-
time-out" period .
client-error-request-entity-too-large: same as Print-Job.
client-error-conflicting-attributes: same as Print-Job, except
that "ipp-attributes-fidelity" operation attribute is not
involved..
server-error-operation-not-supported: the Send-Document
request is not supported.
server-error-not-accepting-jobs: not applicable.
server-error-job-canceled: the job has been canceled by an
operator or the system while the client was transmitting the
data.
3.1.3.2.2 Send-URI
All of the Print-Job status code descriptions in Section 3.1.3.1.1
Print-Job Response with the specialization's described for Send-
Document are applicable to Send-URI. See Section 13 in [RFC2911] for
a more complete description of each status code.
client-error-uri-scheme-not-supported: the URI scheme supplied
in the "document-uri" operation attribute is not supported and
the "document-uri" attribute MUST be returned in the
Unsupported Attributes group.
server-error-operation-not-supported: the Send-URI operation is
not supported.
3.1.3.2.3 Cancel-Job
All of the Print-Job status codes described in Section 3.1.3.1.1
Print-Job Response are applicable to Cancel-Job with the following
specializations and differences. See Section 13 in [RFC2911] for a
more complete description of each status code.
For the following success status codes, the Job object is being
canceled or has been canceled:
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successful-ok: no request attributes were substituted or
ignored (same as Print-Job).
successful-ok-ignored-or-substituted-attributes: same as
Print-Job.
successful-ok-conflicting-attributes: same as Print-Job.
For any of the error status codes, the Job object has not been
canceled or was previously canceled.
client-error-not-possible: The request cannot be carried out
because of the state of the Job object ('completed',
'canceled', or 'aborted') or the state of the system.
client-error-not-found: the target Printer and/or Job object
does not exist.
client-error-gone: the target Printer and/or Job object no
longer exists and no forwarding address is known.
client-error-request-entity-too-large: same as Print-Job,
except no document data is involved.
client-error-document-format-not-supported: not applicable.
client-error-attributes-or-values-not-supported: not
applicable, since unsupported operation attributes and values
MUST be ignored.
client-error-conflicting-attributes: same as Print-Job, except
that the Printer's "printer-is-accepting-jobs" attribute is not
involved.
server-error-operation-not-supported: not applicable (Cancel-
Job is REQUIRED).
server-error-device-error: same as Print-Job, except no
document data is involved.
server-error-temporary-error: same as Print-Job, except no
document data is involved.
server-error-not-accepting-jobs: not applicable.
server-error-job-canceled: not applicable.
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RFC 3196 Internet Printing Protocol/1.1 November 20013.1.3.2.4 Get-Job-Attributes
All of the Print-Job status codes described in Section 3.1.3.1.1
Print-Job Response are applicable to Get-Job-Attributes with the
following specializations and differences. See Section 13 in
[RFC2911] for a more complete description of each status code.
For the following success status codes, the requested attributes are
returned in Group 3 in the response:
successful-ok: same as Get-Printer-Attributes (see section3.1.3.1.5).
successful-ok-ignored-or-substituted-attributes: same as Get-
Printer-Attributes (see section 3.1.3.1.5).
successful-ok-conflicting-attributes: same as Get-Printer-
Attributes (see section 3.1.3.1.5).
For the error status codes, Group 3 is returned containing no
attributes or is not returned at all.
client-error-not-possible: Same as Print-Job, in addition the
Printer object is not accepting any requests.
client-error-document-format-not-supported: not applicable.
client-error-attributes-or-values-not-supported: not
applicable.
client-error-uri-scheme-not-supported: not applicable.
client-error-attributes-or-values-not-supported: not
applicable, since unsupported operation attributes and/or
values MUST be ignored and an appropriate success code returned
(see above).
client-error-conflicting-attributes: not applicable
server-error-operation-not-supported: not applicable (since
Get-Job-Attributes is REQUIRED).
server-error-device-error: same as Print-Job, except no
document data is involved.
server-error-temporary-error: sane as Print-Job, except no
document data is involved..
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server-error-not-accepting-jobs: not applicable.
server-error-job-canceled: not applicable.
3.1.3.2.5 Hold-Job
All of the Print-Job status codes described in Section 3.1.3.1.1
Print-Job Response are applicable to Hold-Job with the following
specializations and differences. See Section 13 in [RFC2911] for a
more complete description of each status code.
For the following success status codes, the Job object is being held
or has been held:
successful-ok: no request attributes were substituted or
ignored (same as Print-Job).
successful-ok-ignored-or-substituted-attributes: same as
Print-Job.
successful-ok-conflicting-attributes: same as Print-Job.
For any of the error status codes, the Job object has not been held
or was previously held.
client-error-not-possible: The request cannot be carried out
because of the state of the Job object ('completed',
'canceled', or 'aborted') or the state of the system.
client-error-not-found: the target Printer and/or Job object
does not exist.
client-error-gone: the target Printer and/or Job object no
longer exists and no forwarding address is known.
client-error-request-entity-too-large: same as Print-Job,
except no document data is involved.
client-error-document-format-not-supported: not applicable.
client-error-conflicting-attributes: same as Print-Job, except
that the Printer's "printer-is-accepting-jobs" attribute is not
involved.
server-error-operation-not-supported: the Hold-Job operation is
not supported.
server-error-device-error: not applicable.
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server-error-temporary-error: same as Print-Job, except no
document data is involved.
server-error-not-accepting-jobs: not applicable.
server-error-job-canceled: not applicable.
3.1.3.2.6 Release-Job
All of the Print-Job status code descriptions in Section 3.1.3.1.1
Print-Job Response with the specialization's described for Hold-Job
are applicable to Release-Job. See Section 13 in [RFC2911] for a
more complete description of each status code.
server-error-operation-not-supported: the Release-Job operation
is not supported.
3.1.3.2.7 Restart-Job
All of the Print-Job status code descriptions in Section 3.1.3.1.1
Print-Job Response with the specialization's described for Hold-Job
are applicable to Restart-Job. See Section 13 in [RFC2911] for a
more complete description of each status code.
server-error-operation-not-supported: the Restart-Job operation
is not supported.
3.1.3.2.7.1 Can documents be added to a restarted job?
Assume I give a Create-Job request along with a set of 5 documents.
All the documents get printed and the job state is moved to
completed. I issue a Restart-Job request on the job. Now the issue
is that, if I try to add new documents to the restarted job, will the
IPP Server permit me to do so or return "client-error-not-possible "
and again print those 5 jobs?
A job can not move to the 'completed' state until all the documents
have been processed. The 'last-document' flag indicates when the
last document for a job is being sent from the client. This is the
semantic equivalent of closing a job. No documents may be added once
a job is closed. Section 3.3.7 of the IPP/1.1 model states "The job
is moved to the 'pending' job state and restarts the beginning on the
same IPP Printer object with the same attribute values." 'number-
of-documents' is a job attribute.
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RFC 3196 Internet Printing Protocol/1.1 November 20013.1.4 Returning unsupported attributes in Get-Xxxx responses (Issue 1.18)
In the Get-Printer-Attributes, Get-Jobs, or Get-Job-Attributes
responses, the client cannot depend on getting unsupported attributes
returned in the Unsupported Attributes group that the client
requested, but are not supported by the IPP object. However, such
unsupported requested attributes will not be returned in the Job
Attributes or Printer Attributes group (since they are unsupported).
Furthermore, the IPP object is REQUIRED to return the 'successful-
ok-ignored-or-substituted-attributes' status code, so that the client
knows that not all that was requested has been returned.
3.1.5 Sending empty attribute groups
The [RFC2911] and [RFC2910] specifications RECOMMEND that a sender
not send an empty attribute group in a request or a response.
However, they REQUIRE a receiver to accept an empty attribute group
as equivalent to the omission of that group. So a client SHOULD omit
the Job Template Attributes group entirely in a create operation that
is not supplying any Job Template attributes. Similarly, an IPP
object SHOULD omit an empty Unsupported Attributes group if there are
no unsupported attributes to be returned in a response.
The [RFC2910] specification REQUIRES a receiver to be able to receive
either an empty attribute group or an omitted attribute group and
treat them equivalently. The term "receiver" means an IPP object for
a request and a client for a response. The term "sender' means a
client for a request and an IPP object for a response.
There is an exception to the rule for Get-Jobs when there are no
attributes to be returned. [RFC2910] contains the following
paragraph:
The syntax allows an xxx-attributes-tag to be present when the xxx-
attribute-sequence that follows is empty. The syntax is defined this
way to allow for the response of Get-Jobs where no attributes are
returned for some job-objects. Although it is RECOMMENDED that the
sender not send an xxx-attributes-tag if there are no attributes
(except in the Get-Jobs response just mentioned), the receiver MUST
be able to decode such syntax.
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RFC 3196 Internet Printing Protocol/1.1 November 20013.2 Printer Operations3.2.1 Print-Job operation3.2.1.1 Flow controlling the data portion of a Print-Job request (Issue 1.22)
A paused printer, or one that is stopped due to paper out or jam or
spool space full or buffer space full, may flow control the data of a
Print-Job operation (at the TCP/IP layer), so that the client is not
able to send all the document data. Consequently, the Printer will
not return a response until the condition is changed.
The Printer should not return a Print-Job response with an error code
in any of these conditions, since either the printer will be resumed
and/or the condition will be freed either by human intervention or as
jobs print.
In writing test scripts to test IPP Printers, the script must also be
written not to expect a response, if the printer has been paused,
until the printer is resumed, in order to work with all possible
implementations.
3.2.1.2 Returning job-state in Print-Job response (Issue 1.30)
An IPP client submits a small job via Print-Job. By the time the IPP
printer/print server is putting together a response to the operation,
the job has finished printing and been removed as an object from the
print system. What should the job-state be in the response?
The Model suggests that the Printer return a response before it even
accepts the document content. The Job Object Attributes are returned
only if the IPP object returns one of the success status codes. Then
the job-state would always be "pending" or "pending-held".
This issue comes up for the implementation of an IPP Printer object
as a server that forwards jobs to devices that do not provide job
status back to the server. If the server is reasonably certain that
the job completed successfully, then it should return the job-state
as 'completed'. Also the server can keep the job in its "job
history" long after the job is no longer in the device. Then a user
could query the server and see that the job was in the 'completed'
state and completed as specified by the jobs "time-at-completed"
time, which would be the same as the server submitted the job to the
device.
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An alternative is for the server to respond to the client before or
while sending the job to the device, instead of waiting until the
server has finished sending the job to the device. In this case, the
server can return the job's state as 'pending' with the 'job-
outgoing' value in the job's "job-state-reasons" attribute.
If the server doesn't know for sure whether the job completed
successfully (or at all), it could return the (out-of-band) 'unknown'
value.
On the other hand, if the server is able to query the device and/or
setup some sort of event notification that the device initiates when
the job makes state transitions, then the server can return the
current job state in the Print-Job response and in subsequent queries
because the server knows what the job state is in the device (or can
query the device).
All of these alternatives depend on implementation of the server and
the device.
3.2.2 Get-Printer-Attributes operation
If a Printer supports the "printer-make-and-model" attribute and
returns the .INF file model name of the printer in that attribute,
the Microsoft client will automatically install the correct driver
(if available).
Clients which poll periodically for printer status or queued-job-
count should use the "requested-attributes" operation attribute to
limit the scope of the query in order to save Printer and network
resources.
3.2.3 Get-Jobs operation3.2.3.1 Get-Jobs, my-jobs='true', and 'requesting-user-name' (Issue 1.39)?
In [RFC2911] section 3.2.6.1 'Get-Jobs Request', if the attribute
'my-jobs' is present and set to TRUE, MUST the 'requesting-user-name'
attribute be there too, and if it's not present what should the IPP
printer do?
[RFC2911] Section 8.3 describes the various cases of "requesting-
user-name" being present or not for any operation. If the client
does not supply a value for "requesting-user-name", the printer MUST
assume that the client is supplying some anonymous name, such as
"anonymous".
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RFC 3196 Internet Printing Protocol/1.1 November 20013.2.3.2 Why is there a "limit" attribute in the Get-Jobs operation?
When using the Get-Jobs operation a client implementer might choose
to limit the number of jobs that the client shows on the first
screenful. For example, if its UI can only display 50 jobs, it can
defend itself against a printer that would otherwise return 500 jobs,
perhaps taking a long time on a slow dial-up line. The client can
then go and ask for a larger number of jobs in the background, while
showing the user the first 50 jobs. Since the job history is returned
in reverse order, namely the most recently completed jobs are
returned first, the user is most likely interested in the first jobs
that are returned. Limiting the number of jobs may be especially
useful for a client that is requesting 'completed' jobs from a
printer that keeps a long job history. Clients that don't mind
sometimes getting very large responses, can omit the "limit"
attribute in their Get-Jobs requests.
3.2.4 Create-Job operation
A Printer may respond to a Create-Job operation with "job-state"
'pending' or 'pending-held' and " job-state-reason" 'job-data-
insufficient' to indicate that operation has been accepted by the
Printer, but the Printer is expecting additional document data before
it can move the job into the 'processing' state. Alternatively, it
may respond with "job-state" 'processing' and "job-state-reason"
'job-incoming' to indicate that the Create-Job operation has been
accepted by the Printer, but the Printer is expecting additional
Send-Document and/or Send-URI operations and/or is
accessing/accepting document data. The second alternative is for
non-spooling Printers that don't implement the 'pending' state.
Should the server wait for the "last-document" operation attribute
set to 'true' before starting to "process" the job?
It depends on implementation. Some servers spool the entire job,
including all document data, before starting to process, so such an
implementation would wait for the "last-document" before starting to
process the job. If the time-out occurs without the "last-document",
then the server takes one of the indicated actions in section 3.3.1
in the [RFC2911] document. Other servers will start to process
document data as soon as they have some. These are the so-called
"non-spooling" printers. Currently, there isn't a way for a client to
determine whether the Printer will spool all the data or will start
to process (and print) as soon as it has some data.
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RFC 3196 Internet Printing Protocol/1.1 November 20013.3 Job Operations3.3.1 Validate-Job
The Validate-Job operation has been designed so that its
implementation may be a part of the Print-Job operation. Therefore,
requiring Validate-Job is not a burden on implementers. Also it is
useful for client's to be able to count on its presence in all
conformance implementations, so that the client can determine before
sending a long document, whether the job will be accepted by the IPP
Printer or not.
3.3.2 Restart-Job
The Restart-Job operation allows the reprocessing of a completed job.
Some jobs store the document data on the printer. Jobs created using
the Print-Job operation are an example. It is required that the
printer retains the job data after the job has moved to a 'completed
state' in order for the Restart-Job operation to succeed.
Some jobs contain only a reference to the job data. A job created
using the Print-URI is an example of such a job. When the Restart-
Job operation is issued the job is reprocessed. The job data MUST be
retrieved again to print the job.
It is possible that a job fails while attempting to access the print
data. When such a job is the target of a Restart-Job the Printer
SHALL attempt to retrieve the job data again.
4 Object Attributes4.1 Attribute Syntax's4.1.1 The 'none' value for empty sets (Issue 1.37)
[RFC2911] states that the 'none' value should be used as the value of
a 1setOf when the set is empty. In most cases, sets that are
potentially empty contain keywords so the keyword 'none' is used, but
for the 3 finishings attributes, the values are enums and thus the
empty set is represented by the enum 3. Currently there are no other
attributes with 1setOf values, which can be empty and can contain
values that are not keywords. This exception requires special code
and is a potential place for bugs. It would have been better if we
had chosen an out-of-band value, either "no-value" or some new value,
such as 'none'. Since we didn't, implementations have to deal with
the different representations of 'none', depending on the attribute
syntax.
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RFC 3196 Internet Printing Protocol/1.1 November 20014.1.2 Multi-valued attributes (Issue 1.31)
What is the attribute syntax for a multi-valued attribute? Since
some attributes support values in more than one data type, such as
"media", "job-hold-until", and "job-sheets", IPP semantics associate
the attribute syntax with each value, not with the attribute as a
whole. The protocol associates the attribute syntax tag with each
value. Don't be fooled, just because the attribute syntax tag comes
before the attribute keyword. All attribute values after the first
have a zero length attribute keyword as the indication of a
subsequent value of the same attribute.
4.1.3 Case Sensitivity in URIs (issue 1.6)
IPP client and server implementations must be aware of the diverse
uppercase/lowercase nature of URIs. RFC 2396 defines URL schemes and
Host names as case insensitive but reminds us that the rest of the
URL may well demonstrate case sensitivity. When creating URL's for
fields where the choice is completely arbitrary, it is probably best
to select lower case. However, this cannot be guaranteed and
implementations MUST NOT rely on any fields being case-sensitive or
case-insensitive in the URL beyond the URL scheme and host name
fields.
The reason that the IPP specification does not make any restrictions
on URIs, is so that implementations of IPP may use off-the-shelf
components that conform to the standards that define URIs, such as
RFC 2396 and the HTTP/1.1 specifications [RFC2616]. See these
specifications for rules of matching, comparison, and case-
sensitivity.
It is also recommended that System Administrators and implementations
avoid creating URLs for different printers that differ only in their
case. For example, don't have Printer1 and printer1 as two different
IPP Printers.
Example of equivalent URI's
http://abc.com:80/~smith/home.htmlhttp://ABC.com/%7Esmith/home.html
http:/ABC.com:/%7esmith/home.html
Example of equivalent URI's using the IPP scheme
ipp://abc.com:631/~smith/home.html
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ipp://ABC.com/%7Esmith/home.html
http:/ABC.com:631/%7esmith/home.html
The HTTP/1.1 specification [RFC2616] contains more details on
comparing URLs.
4.1.4 Maximum length for xxxWithLanguage and xxxWithoutLanguage
The 'textWithLanguage' and 'nameWithLanguage' are compound syntaxes
that have two components. The first component is the 'language'
component that can contain up to 63 octets. The second component is
the 'text' or 'name' component. The maximum length of these are 1023
octets and 255 octets respectively. The definition of attributes
with either syntax may further restrict the length (e.g., printer-
name (name(127))).
The length of the 'language' component has no effect on the allowable
length of 'text' in 'textWithLanguage' or the length of 'name' in
'nameWithLanguage'
4.2 Job Template Attributes4.2.1 multiple-document-handling(type2 keyword)4.2.1.1 Support of multiple document jobs
IPP/1.0 is silent on which of the four effects an implementation
would perform if it supports Create-Job, but does not support
"multiple-document-handling" or multiple documents per job. IPP/1.1
was changed so that a Printer could support Create-Job without having
to support multiple document jobs. The "multiple-document-jobs-
supported" (boolean) Printer description attribute was added to
IPP/1.1 along with the 'server-error-multiple-document-jobs-not-
supported' status code for a Printer to indicate whether or not it
supports multiple document jobs, when it supports the Create-Job
operation. Also IPP/1.1 was clarified that the Printer MUST support
the "multiple-document-handling" (type2 keyword) Job Template
attribute with at least one value if the Printer supports multiple
documents per job.
4.3 Job Description Attributes4.3.1 Getting the date and time of day
The "date-time-at-creation", "date-time-at-processing", and "date-
time-at-completed" attributes are returned as dateTime syntax. These
attributes are OPTIONAL for a Printer to support. However, there are
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RFC 3196 Internet Printing Protocol/1.1 November 2001
various ways for a Printer to get the date and time of day. Some
suggestions:
1. A Printer can get time from an NTP timeserver if there's one
reachable on the network . See RFC 1305. Also DHCP option 32
in RFC 2132 returns the IP address of the NTP server.
2. Get the date and time at startup from a human operator
3. Have an operator set the date and time using a web
administrative interface
4. Get the date and time from incoming HTTP requests, though the
problems of spoofing need to be considered. Perhaps comparing
several HTTP requests could reduce the chances of spoofing.
5. Internal date time clock battery driven.
6. Query "http://tycho.usno.navy.mil/cgi-bin/timer.pl"
4.4 Printer Description Attributes4.4.1 queued-job-count (integer(0:MAX))4.4.1.1 Why is "queued-job-count" RECOMMENDED (Issue 1.14)?
The reason that "queued-job-count" is RECOMMENDED, is that some
clients look at that attribute alone when summarizing the status of a
list of printers, instead of doing a Get-Jobs to determine the number
of jobs in the queue. Implementations that fail to support the
"queued-job-count" will cause that client to display 0 jobs when
there are actually queued jobs.
We would have made it a REQUIRED Printer attribute, but some
implementations had already been completed before the issue was
raised, so making it a SHOULD was a compromise.
4.4.1.2 Is "queued-job-count" a good measure of how busy a printer is
(Issue 1.15)?
The "queued-job-count" is not a good measure of how busy the printer
is when there are held jobs. A future registration could be to add a
"held-job-count" (or an "active-job-count") Printer Description
attribute if experience shows that such an attribute (combination) is
needed to quickly indicate how busy a printer really is.
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RFC 3196 Internet Printing Protocol/1.1 November 20014.4.2 printer-current-time (dateTime)
A Printer implementation MAY support this attribute by obtaining the
date and time by any number of implementation-dependent means at
startup or subsequently. Examples include:
1. an internal date time clock,
2. from the operator at startup using the console,
3. from an operator using an administrative web page,
4. from HTTP headers supplied in client requests,
5. use HTTP to query "http://tycho.usno.navy.mil/cgi-bin/timer.pl"
6. from the network, using NTP [RFC1305] or DHCP option 32
[RFC2132] that returns the IP address of the NTP server.
If an implementation supports this attribute by obtaining the current
time from the network (at startup or later), but the time is not
available, then the implementation MUST return the value of this
attribute using the out-of-band 'no-value' meaning not configured.
See the beginning of section 4.1.
Since the new "date-and-time-at-xxx" Job Description attributes refer
to the "printer-current-time", they will be covered also.
4.4.3 Printer-uri
Must the operational attribute for printer-uri match one of the
values in "printer-uri-supported"?
A forgiving printer implementation would not reject the operation.
But the implementation has its rights to reject a printer or job
operation if the operational attribute printer-uri is not a value of
the printer-uri-supported. The printer might not be improperly
configured. The request obviously reached the printer. The printer
could treat the printer-uri as the logical equivalent of a value in
the printer-uri-supported. It would be implementation dependent for
which value, and associated security policy, would apply. This does
also apply to a job object specified with a printer-uri and job-id,
or with a job-uri. See section 4.1.3 for how to compare URI's.
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RFC 3196 Internet Printing Protocol/1.1 November 20014.5 Empty Jobs
The IPP object model does not prohibit a job that contains no
documents. Such a job may be created in a number of ways including a
'create-job' followed by an 'add-document' that contains no data and
has the 'last-document' flag set.
An empty job is processed just as any other job. The operation that
"closes" an empty job is not rejected because the job is empty. If
no other conditions exist, other than the job is empty, the response
to the operation will indicate success. After the job is scheduled
and processed, the job state SHALL be 'completed'.
There will be some variation in the value(s) of the "job-state-
reasons" attribute. It is required that if no conditions, other than
the job being empty, exist the "job-state-reasons" SHALL include the
'completed-successfully'. If other conditions existed, the
'completed-with-warnings' or 'completed-with-errors' values may be
used.
5 Directory Considerations5.1 General Directory Schema Considerations
The [RFC2911] document lists RECOMMENDED and OPTIONAL Printer object
attributes for directory schemas. See [RFC2911] APPENDIX E: Generic
Directory Schema.
The SLP printer template is defined in the "Definition of the Printer
Abstract Service Type v2.0" document [svrloc-printer]. The LDAP
printer template is defined in the "Internet Printing Protocol (IPP):
LDAP Schema for Printer Services" document [ldap-printer]. Both
documents systematically add "printer-" to any attribute that doesn't
already start with "printer-" in order to keep the printer directory
attributes distinct from other directory attributes. Also, instead
of using "printer-uri-supported", "uri-authentication-supported", and
"uri-security-supported", they use a "printer-xri-supported"
attribute with special syntax to contain all of the same information
in a single attribute.
5.2 IPP Printer with a DNS name
If the IPP printer has a DNS name should there be at least two values
for the printer-uri-supported attribute. One URL with the fully
qualified DNS name the other with the IP address in the URL?
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The printer may contain one or the other or both. It's up to the
administrator to configure this attribute.
6 Security Considerations
The security considerations given in [RFC2911] Section 8 "Security
Considerations" all apply to this document. In addition, the
following sub-sections describes security consideration that have
arisen as a result of implementation testing.
6.1 Querying jobs with IPP that were submitted using other job submission protocols (Issue 1.32)
The following clarification was added to [RFC2911] section 8.5:
8.5 Queries on jobs submitted using non-IPP protocols If the
device that an IPP Printer is representing is able to accept jobs
using other job submission protocols in addition to IPP, it is
RECOMMEND that such an implementation at least allow such
"foreign" jobs to be queried using Get-Jobs returning "job-id" and
"job-uri" as 'unknown'. Such an implementation NEED NOT support
all of the same IPP job attributes as for IPP jobs. The IPP
object returns the 'unknown' out-of-band value for any requested
attribute of a foreign job that is supported for IPP jobs, but not
for foreign jobs.
It is further RECOMMENDED, that the IPP Printer generate "job-id"
and "job-uri" values for such "foreign jobs", if possible, so that
they may be targets of other IPP operations, such as Get-Job-
Attributes and Cancel-Job. Such an implementation also needs to
deal with the problem of authentication of such foreign jobs. One
approach would be to treat all such foreign jobs as belonging to
users other than the user of the IPP client. Another approach
would be for the foreign job to belong to 'anonymous'. Only if
the IPP client has been authenticated as an operator or
administrator of the IPP Printer object, could the foreign jobs be
queried by an IPP request. Alternatively, if the security policy
were to allow users to query other users' jobs, then the foreign
jobs would also be visible to an end-user IPP client using Get-
Jobs and Get-Job- Attributes.
Thus IPP MAY be implemented as a "universal" protocol that
provides access to jobs submitted with any job submission
protocol. As IPP becomes widely implemented, providing a more
universal access makes sense.
Hastings, et al. Informational [Page 80]

RFC 3196 Internet Printing Protocol/1.1 November 20017 Encoding and Transport
This section discusses various aspects of IPP/1.1 Encoding and
Transport [RFC2910].
A server is not required to send a response until after it has
received the client's entire request. Hence, a client must not
expect a response until after it has sent the entire request.
However, we recommend that the server return a response as soon as
possible if an error is detected while the client is still sending
the data, rather than waiting until all of the data is received.
Therefore, we also recommend that a client listen for an error
response that an IPP server MAY send before it receives all the data.
In this case a client, if chunking the data, can send a premature
zero-length chunk to end the request before sending all the data (and
so the client can keep the connection open for other requests, rather
than closing it). If the request is blocked for some reason, a
client MAY determine the reason by opening another connection to
query the server using Get-Printer-Attributes.
IPP, by design, uses TCP's built-in flow control mechanisms [RFC 793]
to throttle clients when Printers are busy. Therefore, it is
perfectly normal for an IPP client transmitting a Job to be blocked
for a really long time. Accordingly, socket timeouts must be
avoided. Some socket implementations have a timeout option, which
specifies how long a write operation on a socket can be blocked
before it times out and the blocking ends. A client should set this
option for infinite timeout when transmitting Job submissions.
Some IPP client applications might be able to perform other useful
work while a Job transmission is blocked. For example, the client
may have other jobs that it could transmit to other Printers
simultaneously. A client may have a GUI, which must remain
responsive to the user while the Job transmission is blocked. These
clients should be designed to spawn a thread to handle the Job
transmission at its own pace, leaving the main application free to do
other work. Alternatively, single-threaded applications could use
non-blocking I/O.
Some Printer conditions, such as jam or lack of paper, could cause a
client to be blocked indefinitely. Clients may open additional
connections to the Printer to Get-Printer-Attributes, determine the
state of the device, alert a user if the printer is stopped, and let
a user decide whether to abort the job transmission or not.
In the following sections, there are tables of all HTTP headers,
which describe their use in an IPP client or server. The following
is an explanation of each column in these tables.
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RFC 3196 Internet Printing Protocol/1.1 November 2001
- the "header" column contains the name of a header
- the "request/client" column indicates whether a client sends the
header.
- the "request/ server" column indicates whether a server supports
the header when received.
- the "response/ server" column indicates whether a server sends
the header.
- the "response /client" column indicates whether a client
supports the header when received.
- the "values and conditions" column specifies the allowed header
values and the conditions for the header to be present in a
request/response.
The table for "request headers" does not have columns for responses,
and the table for "response headers" does not have columns for
requests.
The following is an explanation of the values in the "request/client"
and "response/ server" columns.
- must: the client or server MUST send the header,
- must-if: the client or server MUST send the header when the
condition described in the "values and conditions" column is
met,
- may: the client or server MAY send the header
- not: the client or server SHOULD NOT send the header. It is not
relevant to an IPP implementation.
The following is an explanation of the values in the
"response/client" and "request/ server" columns.
- must: the client or server MUST support the header,
- may: the client or server MAY support the header
- not: the client or server SHOULD NOT support the header. It is
not relevant to an IPP implementation.
Hastings, et al. Informational [Page 82]

RFC 3196 Internet Printing Protocol/1.1 November 20017.1 General Headers
The following is a table for the general headers.
General- Request Response Values and Conditions
Header
Client Server Server Client
Cache- not must not "no-cache" only
Control must
Connection must- must must- must "close" only. Both
if if client and server
SHOULD keep a
connection for the
duration of a sequence
of operations. The
client and server MUST
include this header
for the last operation
in such a sequence.
Date may may must may per RFC 1123 [RFC1123]
from RFC 2616
[RFC2616]
Pragma must not must not "no-cache" only
Transfer- must- must must- must "chunked" only. Header
Encoding if if MUST be present if
Content-Length is
absent.
Upgrade not not not not
Via not not not not
Hastings, et al. Informational [Page 83]

RFC 3196 Internet Printing Protocol/1.1 November 20017.2 Request Headers
The following is a table for the request headers.
Request- Client Server Request Values and Conditions
Header
Accept may must "application/ipp" only. This
value is the default if the
client omits it
Accept- not not Charset information is within the
Charset application/ipp entity
Accept- may must empty and per RFC 2616 [RFC2616]
Encoding and IANA registry for content-
codings
Accept- not not language information is within the
Language application/ipp entity
Authorization must- must per RFC 2616. A client MUST send
if this header when it receives a
401 "Unauthorized" response and
does not receive a "Proxy-
Authenticate" header.
From not not per RFC 2616. Because RFC
recommends sending this header
only with the user's approval,
it is not very useful
Host must must per RFC 2616
If-Match not not
If-Modified- not not
Since
If-None-Match not not
If-Range not not
If- not not
Unmodified-
Since
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RFC 3196 Internet Printing Protocol/1.1 November 2001
Request- Client Server Request Values and Conditions
Header
Max-Forwards not not
Proxy- must- not per RFC 2616. A client MUST send
Authorizati if this header when it receives a
on 401 "Unauthorized" response and
a "Proxy-Authenticate" header.
Range not not
Referrer not not
User-Agent not not
Hastings, et al. Informational [Page 85]

RFC 3196 Internet Printing Protocol/1.1 November 20017.3 Response Headers
The following is a table for the request headers.
Response- Server Client Response Values and Conditions
Header
Accept-Ranges not not
Age not not
Location must- may per RFC 2616. When URI needs
if redirection.
Proxy- must per RFC 2616
Authenticat
e not
Public may may per RFC 2616
Retry-After may may per RFC 2616
Server not not
Vary not not
Warning may may per RFC 2616
WWW- must- must per RFC 2616. When a server needs
Authenticate if to authenticate a client.
Hastings, et al. Informational [Page 86]

RFC 3196 Internet Printing Protocol/1.1 November 20017.4 Entity Headers
The following is a table for the entity headers.
Entity-Header Request Response Values and
Conditions
Client Server Server Client
Allow not not not not
Content-Base not not not not
Content- may must must must per RFC 2616 and
Encoding IANA registry for
content codings.
Content- not not not not Application/ipp
Language handles language
Content- must- must must- must the length of the
Length if if message-body per
RFC 2616. Header
MUST be present
if Transfer-
Encoding is
absent..
Content- not not not not
Location
Content-MD5 may may may may per RFC 2616
Content-Range not not not not
Content-Type must must must must "application/ipp"
only
ETag not not not not
Expires not not not not
Last-Modified not not not not
Hastings, et al. Informational [Page 87]

RFC 3196 Internet Printing Protocol/1.1 November 20017.5 Optional support for HTTP/1.0
IPP implementations consist of an HTTP layer and an IPP layer. In
the following discussion, the term "client" refers to the HTTP client
layer and the term "server" refers to the HTTP server layer. The
Encoding and Transport document [RFC2910] requires that HTTP 1.1 MUST
be supported by all clients and all servers. However, a client
and/or a server implementation may choose to also support HTTP 1.0.
This option means that a server may choose to communicate with a
(non-conforming) client that only supports HTTP 1.0. In such cases
the server should not use any HTTP 1.1 specific parameters or
features and should respond using HTTP version number 1.0.
This option also means that a client may choose to communicate with a
(non-conforming) server that only supports HTTP 1.0. In such cases,
if the server responds with an HTTP 'unsupported version number' to
an HTTP 1.1 request, the client should retry using HTTP version
number 1.0.
7.6 HTTP/1.1 Chunking7.6.1 Disabling IPP Server Response Chunking
Clients MUST anticipate that the HTTP/1.1 server may chunk responses
and MUST accept them in responses. However, a (non-conforming) HTTP
client that is unable to accept chunked responses may attempt to
request an HTTP 1.1 server not to use chunking in its response to an
operation by using the following HTTP header:
TE: identity
This mechanism should not be used by a server to disable a client
from chunking a request, since chunking of document data is an
important feature for clients to send long documents.
7.6.2 Warning About the Support of Chunked Requests
This section describes some problems with the use of chunked requests
and HTTP/1.1 servers.
The HTTP/1.1 standard [RFC2616] requires that conforming servers
support chunked requests for any method. However, in spite of this
requirement, some HTTP/1.1 implementations support chunked responses
in the GET method, but do not support chunked POST method requests.
Some HTTP/1.1 implementations that support CGI scripts [CGI] and/or
servlets [Servlet] require that the client supply a Content-Length.
These implementations might reject a chunked POST method and return a
Hastings, et al. Informational [Page 88]

RFC 3196 Internet Printing Protocol/1.1 November 2001
included in a printing protocol for the Internet. It identifies
requirements for three types of users: end users, operators, and
administrators. It calls out a subset of end user requirements that
are satisfied in IPP/1.0 [RFC2566, RFC2565]. A few OPTIONAL operator
operations have been added to IPP/1.1 [RFC2911, RFC2910].
The "Rationale for the Structure and Model and Protocol for the
Internet Printing Protocol" document describes IPP from a high level
view, defines a roadmap for the various documents that form the suite
of IPP specification documents, and gives background and rationale
for the IETF IPP working group's major decisions.
The "Internet Printing Protocol/1.1: Model and Semantics" document
describes a simplified model with abstract objects, their attributes,
and their operations. The model introduces a Printer and a Job. The
Job supports multiple documents per Job. The model document also
addresses how security, internationalization, and directory issues
are addressed.
The "Internet Printing Protocol/1.1: Encoding and Transport" document
is a formal mapping of the abstract operations and attributes defined
in the model document onto HTTP/1.1 [RFC2616]. It also defines the
encoding rules for a new Internet MIME media type called
"application/ipp". This document also defines the rules for
transporting a message body over HTTP whose Content-Type is
"application/ipp". This document defines the 'ipp' scheme for
identifying IPP printers and jobs.
The "Mapping between LPD and IPP Protocols" document gives some
advice to implementers of gateways between IPP and LPD (Line Printer
Daemon) implementations.
Hastings, et al. Informational [Page 95]

RFC 3196 Internet Printing Protocol/1.1 November 200111 Full Copyright Statement
Copyright (C) The Internet Society (2001). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
Hastings, et al. Informational [Page 96]